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THE FOOT'S ROLE IN SKIING (the work of David McPhail)

post #1 of 28
Thread Starter 

Several years ago a special person found his way to Epicski, and shared with us his work on how the bio-mechanics of the foot can be used to promote the realization of great skiing, and the role the design and proper set-up of a ski boot plays.  

 

David's background in the industry was vast, having worked with Canada's National Team, working on the development of an all new type of ski boot, running cutting edge testing, and if memory serves, speaking at the International Congress on Science & Skiing in St. Christoph (St. Anton), Austria.

 

His postings here at Epic were fascinating, and a few of us later formed a think tank study group with David, to continue exploration of the subject matter.  I think it would be worthwhile to revisit David's work, as it still as relevant and valuable now as it was back then.  

 

We're fortunate that a past member/supporter of Epicski, Little Tiger (aka Janis Williams) had the foresight when the conversations were taking place, to extract David's contributions from the silliness that tends to clutter up discussions here, and compile them into a 3 page thread.  It was a massive job, and because of Janis's work we now have easy access to the entirety of David's writings here at Epic.  

 

Have a read, but be forewarned, it's going to take you some time, but it will be worth the investment for those who are truly interested in exploring in depth the role of the foot and the ski boot in our sport.  

 

 

post #2 of 28
Thread Starter 

 

SECTION 1
 
 
 
Quote:
Originally posted by David M:
“A curious thing about balance is that people usually expect to find that balancing is a fairly simple process, since nearly everyone can perform the routine balancing acts of everyday existence, without having think about what they are doing. In fact, the more one looks into it, the more complex and mysterious balancing behavior becomes.” 
Understanding Balance – The Mechanics of Posture and Locomotion by Tristan D. M. Roberts.

...Studies done at the University of Calgary’s Human Performance Laboratory have conclusively shown that our feet function best when bare. I did experimental research on balance in skiing back in 1991 with an instrumented device that replaced the ski boot. The device allowed the parameters of constraint applied to the foot and leg to be varied in a systematic manner and the effects on balance measured during typical ski maneuvers. The results were very interesting. When an environment conducive to the natural processes of balance was created all good skiers (including former Olympians) used essentially the same balance mechanisms. Even more interesting was that novice skiers started to use the very same mechanisms after only a few short runs -- with no coaching! 

One of the challenges to the balance system that makes skiing difficult is that our vertical reference keeps changing. When it does the brain has a hard time figuring out which way is up. This is called behavioral vertical. If a novice starts off on a flat section of a ski run with both skis flat on the snow vertical will be vertical to the force of gravity. But as soon as that person pushes over the edge and starts down a slope behavioral vertical will change. Until such time as the skier learns to make a positive move to change the vertical reference the righting reflex will override behavioral vertical and try to maintain its reference with gravity. The result will be that the normal balance response intended to restore the vertical alignment will cause the novice to sit back.

Further exacerbating this situation is the fact that constraint imposed on the foot and leg by the ski boot can contaminate the processes that give the balance system information critical to balance. Garbage in, garbage out. In addition ski boots and related equipment typically prevent our feet from establishing the relationship with the snow (the ground) associated with our normal processes of balance. The result is that something we normally perform with such efficiency that it belies it belies its real complexity becomes a foreign, unfamiliar, unnatural ineffective process. Balance exercises will not significantly improve this core aspect of balance.

More later.
 
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#2
Quote:
Originally posted by David M:
“Three major sensory systems are involved in balance and posture. Vision is the system that is primarily involved in planning our locomotion (read: movement) and in avoiding obstacles along the way. The vestibular system (i.e. chambers in the inner ear) is our “gyro” which senses linear and angular accelerations. The somatosensory system (whole body) is a multitude of sensors which sense the position and velocity of all body segments, their contact (impact) with external objects (including the ground [or lack of contact with the ground – David M]) and the orientation of gravity (or forces that act in a similar manner). Neurophysiologists have devised a wide range of experiments to tease out the contribution of each of these systems and even to confuse the system by providing conflicting or false sensory input [this is what a ski boot typically does – David M]. However, when sensory conflict between visual and somatosensory information occurs the vestibular system intervenes to resolve the conflict. 

“There are some suggestions that that there is a fourth source of afferent (conducting toward a center) information that informs the CNS (central nervous system) about body weight or gravity. The suggested receptors are the Golgi tendon organs, so this may be a special form of proprioception that may be devoted to calculating the location of the total body COG (in space). As will be seen in many examples, ranging from quiet standing to termination of gait, there is strong evidence from detailed motor patterns that the CNS is continuously calculating the location of the body’s center of gravity (COG).

“Postural and balance adjustments, either reactive or proactive, are characterized by coordinated motor patterns at many joints. The timing and amplitude of these patterns are described as strategies or synergies. For example, perturbations (forces that tend to disrupt balance) to the base of support result in a “bottom-up” sequence of latencies: plantarflexors (the foot pushes down) followed by knee flexors, followed by hip extensors and paraspinal muscles.

“When a researcher is interested in reactive responses he/she introduces unexpected perturbations. On the other hand, proactive control will require either voluntarily initiated internal perturbations (such as raising an arm) or anticipatory well learnt perturbations such as experienced many times over the walking [or skiing – David M] cycle.”

A.B.C (Anatomy, Biomechanics and Control of Balance During Standing and Walking) – David A. Winter, University of Waterloo, Waterloo, Ontario, Canada (Waterloo Biomechanics, 1995)

The implications of the above for skiing are as follows: If you disrupt the normal bottom-up balance response, which is predominantly somatosensory in nature, the vestibular system will intervene (i.e. take control of the balance system) in an effort to restore balance. The vestibular system is a top-down response as opposed to the primary balance system, which is bottom-up; i.e. feet first. As such, the vestibular system uses very little information relating to the position or integrity of the base of support at the feet. The reason for this is that the balance system has interpreted a failure of the bottom-up system. So the vestibular system can never create true balance where it counts – at the interface between the feet and the snow surface. 

If the bottom-up system is prevented from functioning effectively (which is the intended objective of the ski boot) you will typically see a skier try to regain balance in an extended traverse between changes in direction in what amounts to a series of linked recoveries. The reason for this is that they can not initiate a new direction change (they are not turns as such) until they have some semblance of stability. The associated balance strategies typically involve gross body movements and, in particular, gross arm movements. The later are intended to redirect the center of gravity away from the direction of a potential fall

On the other hand, when the primary bottom-up system is functional a skier will only be momentarily out of balance during the transition to the new ski at the start of a new turn. Once this transition is complete the skier will be strongly balanced prior to entering the fall line and will remain so until the completion of the turn where balance is consciously relinquished and transferred to the new outside leg through a process of alternating single limb support. In this context ‘balance’ is defined as “the condition that exists when the sum of the moments of force (turning forces) acting across the joints of the ankle complex at any given time equals zero”. By this I mean that the muscles associated with the joints are able to defend the position of the joint against external forces which tend to disrupt equilibrium. Balance then is an internal response to an external challenge. It is successful if it meets the preceding criteria.

....
 
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#3
Quote:
Originally posted by David M:
...Lisa Marie dynamic balance in skiing implies dynamic balance in erect postures. Normally one would not associate standing with forces that disturb balance. One post likened skiing to standing on the deck of a boat pitching and yawing in the seas. This metaphor is right on the money. In skiing we are standing on 2 distinct bases that are moving over the snow surface in an environment characterized by dynamic forces. This requires that our balance be dynamic in terms of postural balance responses. So, dynamic balance in skiing means dynamic postural balance. This is different from the definition you offer which does necessarily involve postural responses. 

It is also important to recognize that core stability can not be pushed down to the snow surface. My perspective on this issue is that core strength is the conduit that brings the stability of the ground up to the shoulder girdle.

...
 
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#4
Quote:
Originally posted by nolo:
</font><blockquote>quote:</font><hr /> My perspective on this issue is that core strength is the conduit that brings the stability of the ground up to the shoulder girdle.
This is true to my experience and intuition. (I haven't studied this, so all I have is anecdote, experience, and intuition.) The most important feedback is feeling the ground pressing back. This is the touch that Weems talks of that holds up one corner of the total system. 

I really like what you said about the human system being more important than the other equipment, but isn't the issue in skiing that there is the larger system comprised of the human system plus the equipment system, and how do we optimize it? 

How do we assist the vacationer who doesn't have core strength? Can we optimize the system on the equipment side?

I would think the only archetypal motor skill shown by infants at birth is swimming. My mother took me swimming almost every day between the age of 6-14 mos. I swam on my own before I could walk on my own. We are designed for locomotion in the water and on the ground, but not in the air. Our personal evolution mimics the evolution of our species.
</font>[/quote]
 
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#5
Quote:
Originally posted by David M:
I really like what you said about the human system being more important than the other equipment, but isn't the issue in skiing that there is the larger system comprised of the human system plus the equipment system, and how do we optimize it? 

DM: The human system is THE MOST IMPORTANT piece of equipment. The objective is to optimise the entire equipment system. The problem with the current paradigm (and make no mistake, it is a huge problem)is that ski equipment, especially the ski boot, with few exceptions seriously undermines the performance of the cornerstone of the system; the skier

How do we assist the vacationer who doesn't have core strength? Can we optimize the system on the equipment side?
DM: This is the logical place to start. But this can be more difficult and complex than you may realize. We must have both input and influence on equipment design if this is to get easier. There are other things that can help that I will get to in later posts.

I would think the only archetypal motor skill shown by infants at birth is swimming. 
DM: I agree completely. We make learning new skills unnecessarily difficult when we try to use our body in a way it was not designed to be used. I strongly believe this is the main reason why skiing is exceedingly difficult to learn for most people. We can change this by understanding what the body needs to learn. It is much smarter than we are.

We are designed for locomotion in the water and on the ground, but not in the air. 
DM: Agree
 
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#6
Quote:
Originally posted by Ric B:
Correct if I'm wrong but I remember one of the apgar tests is checking for walking movements. We delivered in a birthing with a nurse midwife, and I remember her going through the tests. Remember how new parents compare apgar scores? Anyway, our daughter make the bipedal movements across the table top. And then as I understand it, infants kinda forget until they are ready to walk. My wife and I were just talking about this a couple of days ago. Our daughter is 18 now, but I remember it just like yesterday, actually better than yesterday. Whats that mean? [img]smile.gif[/img] 

Rooted skiing. Yes that's I where I want to go with my skiing this year Nolo. Charlie started this for me at fall festival last year. Then Dweena added to it, but at the time I didn't recognize and put the two together. It's the structural awareness developing from tai chi and the focus received from my instructor that has started tying these various parts together for me. all these things coupled with my understanding and intuitions about balance, are startng to meld into something greater than the parts for me. truly tho for me this goes way back prior to any instructing I've done. whether it's working on slippery surfaces or sliding on them, walking wall plates or treadmills, skinny skiing up new world gultch, or down Mt. ellis, or trying to work and stick to a 9/12 pitch, balance and get something done, our balance is always working and utilizing the same mechanism to achieve and maintain our balance. do we let it or do we fight it. I garanttee that when you're up on a 9/12 trying to get something done, you're thnking and developing your connection, your root. If you can't find a way to direct and focus down to your connection, you might aswell get down and go home, you won't be up there long anyway. I coached many an employee over the mental inhibition, and external focus that kept them from performing at heights. Your body makes the adjustments by recognize and reading the forces. Whether it's centripetal and centrifugal force, wind blowing sideways as you carry a 2x10 rafter up the roof, or an air hose dragging you backwards as you try to go forward, or just walking, our body will find that point of unity if we let it. I don't get the whole concept that we balance different when ski. The forces are for different reasons but still have to be treated the same by our body if we want to achieve that point of unity and we still need to direct everthing into our connection point. I know, I know, we've been here before. [img]graemlins/evilgrin.gif[/img] And everyone that walks to a lesson is capable and has the skills to ski, even many who can't walk or see. Another interesting observation was watching how a seasoned carpenter will change their footwear based on whether they will be on a roof or not. the footwear definetly affects the agility. and it's not just for traction. Good traction only works when you can feel it working. Now I need to get on the snow and play with some things. Care to play Nolo?
 
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#7
Quote:
Originally posted by Lisamarie:
...
Lots of footwear can render the body non functional for skiing, or anything else. The guy who did my foot beds beleives that the aerobic shoes I have worn for close to 30 years of instruction are the reason that my feet need all this corrective work in the ski boot.

On core stability, we speak of it being generated proximally, and sent out distally. It is one part of the equation. But core stability without properly working muscles can be useless.

Great equipment without a properly aligned human body is somewhat ineffective.

....
 
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#8
[quote]Originally posted by Vail Pilgrim:
Three skier-specific bullets on balance:

1. The Skier is in balance when they can have a positive, selective effect on any of the skills with either leg throughout the turn.

2. The entire body is involved and participates in balancing.

3. The focus is on balancing in the future. Keep in mind the difference between movement and motion.

After consulting your dictionary, consider whether or not these statements mean that instruction intended to improve physical skills also improves balance? If so, then isn't teaching balance involved in a large part of ski teaching, even if it's not expressed as an outcome of the lesson?
[/QUOTE
 
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#9
Quote:
Originally posted by David M:
I propose that we accept the following principles as a basis to move forward on a discussion of issues related to balance and movement in skiing:

1. Human function is the primary determinant of skier function in the skier/equipment equation.

2. Sound posture, core strength and their related components are the prerequisites to leveraging human performance.

3. Stable ground is the source of stability and balance in the human system.

4. The degree to which the human system becomes connected or integrated with stable ground directly relates to the efficiency of the internal processes of stability and balance.

5. The archetypal model for balance and movement in skiing is a variation of walking.

6. Balance is the same process for all human activities.

If we agree to these principles we are ready to move to the next step which is a discussion of the theoretical physiological model of the ideal skier. 

The popular notion of proponents of official ski techniques is that the best skiers in the world (i.e. World Cup racers) should serve as the ideal model on which to base technique. But I strongly disagree because while their performance has been shown to be superior we do not know the effects of the conditions that determined their performance. In view of this we do not know the true extend of which their performance reflects their potential. This can only be done by examining the factors under which the human system should ideally perform.
 
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#10
Quote:
Originally posted by David M:
If we accept walking as the archetypal model on which movement in skiing is based we have to also accept that we need to recognize and understand the critical events of walking and how they apply to movement in skiing. These movements occur in the end old turn/initiative new turn phase. The sequence is: initiate right turn – take step-pause----------------initiate left turn – take step - pause -------------- repeat sequence. If you take out the pause (i.e. the arc of the turn) from a photo or video sequence and connect the right and left initiation sequences the walking movements will become apparent.

Nothing about standing on 2 feet and walking is simple. There is a lot of information to assimilate. If you are going to be able to apply this correctly in skiing you have to get it right. I suggest you cut and past the relevant posts into a word processing document so it can be referred to when needed. This is especially important for any principles we agree on. While we can tweak them they must be right. Otherwise we will end up going down the wrong road.

One of the first things we need to know is the different forms of muscle contraction and how they are used in walking and standing. All 3 forms are used in walking, 1 form is used in standing. The muscle actions are: isometric, concentric and eccentric. Does everyone have a crystal clear picture of the differences? If not would Lisa or someone else with the relevant expertise care to explain these. Otherwise I will.
 
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#11
Quote:
Originally posted by Ric B:
Well,

Isometric is a muscle working while staying the same length.
Concentric is a muscle doing work while geting shorter.
Eccentric is a muscle doing work while getting longer.

Keep going. [img]graemlins/thumbsup.gif[/img]
 
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#12
Quote:
Originally posted by David M:
One more thing.

In terms of external energy or shocks from the snow surface being transferred to the lower limbs:

Muscle in concentric contraction is tight, like a bowstring. So it will transmit the energy up the body.

Muscle in eccentric contraction is elastic. So it will absorb the energy and prevent it from being transferred up the body. Under the right conditions muscle in eccentric contraction is capable of absorbing large amounts of energy.
 
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#13
Quote:
Originally posted by David M:
TomB
The answer is eccentric contraction. 

I apologize if I have you hanging on the edge of your seats. But if I do not let others go through the same process I did and arrive at the same conclusions I don’t believe the impact will be nearly as great in terms of imparting an understanding of the issues. This process also helps us all understand where our knowledge is on the issues and where the gaps are. Besides, you are getting the answers right so far. Bear with me and we will soon have enough background information so that I can give you a much bigger picture.

One reason the advantages may not be apparent is that muscles in eccentric contraction can use the stretch reflex. The best description I know of this process can be found in Chapter 36 of Principles of Neural Science (Fourth Edition) by Kandel, Schwartz and Jessell. Don’t try and buy this sucker unless you are wealthy. You can find copies in most medical libraries. I will give you a thumbnail description of how the stretch reflex works later.

In walking, the body uses concentric contraction to put the COG into a position where it can be supported in the stance phase with the muscles in eccentric contraction. The maintenance of an upright posture in both in quiet and perturbed standing relies on eccentric contraction. If you take a side view of a person and draw a line from the center of the ankle joint to the position of the COG in front of the belly button you will see that COG lies in front of the ankle. This creates the tendency for gravity to cause us to fall forward. Muscles in the back of our leg are stretched by gravity. They contract to oppose the forward movement. This is the basic balance strategy. 

RicB (You guys related?)
When we speak of extension and flexion of our legs, to focus on a part, it seems much harder to control the rate or speed of extension. 
DM: If it seems harder to control then you are consciously trying to control muscles. And I suspect that in some most fundamental way your stance may be incorrect. Although we need to make some conscious movements in skiing the sole intent of these movements should be to create the configuration of the body and its relation with the ground (snow = ground) to turn on (and turn up) the unconscious processes of balance. After that you just enjoy the ride until you decide to start a new turn. But it sounds like you are very much into this direction.

RicB: Another thing as I'm thinking of this, eccentric allows the integration of the skeleton in a more effective way also. 
DM: Absolutely!
RicB: How do we get more work done in the top to middle of the turn? 
DM: Not sure what you are getting at here.
RicB: This also ties right into Nolo's idea of the next turn starting in the last third of the previous turn. Circles, eh Nolo? Movements require opposing movements. We have two directions, which can we harness with the most effectiveness, and which give us the best ability to read the forces and respond and stay connected.
DM: When I read things like you said above it just blows me away. Nolo is so on the money it is incredible. The metaphor I like to use is sailing. We set our sails so we can tack across the wind. Once the sails are rigged and the tack established we ride the hell out of the forces acting on us. Then as we approach the turning point we change the sails and set up to tack the other way. 
Sorry I don’t have specific information relating to eccentric power and speed at my fingertips. I used to belong to a biomechanics forum where this issue was regularly discussed. But it has been a few years since I have been there. If I get time later I will do a search. For now I am confident of the power quoted and its relation to acceleration. Perhaps Lisa will have some wisdom for us when she gets off the beach.

I am about to move into a discussion of the physiologic events of walking. We need some references. Lisamarie put up some drawings on another post. Perhaps she can direct us to where they are or repost them. If necessary to impart an understanding I will try and post drawings in the future.

There is a reference system in anatomy called the cardinal planes. They relate to the 3D X, Y, Z axes as in long, transverse and vertical. In anatomy they are called saggital (front to back), frontal (side to side) and coronal (horizontal). In our discussion on balance the front to back or anterior-posterior (a-p) and middle to outside or medial-lateral (m-l) are the most relevant references. I don’t care what we call them so long as everyone gets a clear picture of the issue. If you wish to propose a reference system that you think will be easy for everyone please do so.

Our balance system has to resolve the 2 components (a-p and m-l) simultaneously. In walking (and skiing, as we shall see) it has to plot the a-p, m-l coordinates like the cross hairs of a gun scope and then locate and maintain COG in this target. The normal anatomic relationship that the body tries to establish in standing and walking is with the transverse (horizontal axis) perpendicular to the vertical axis (or one that acts like a vertical axis). While we can stand and walk on tilted surfaces the body tries to avoid prolonged efforts on such mediums because it is inefficient. It makes unconscious choices for us in terms of terrain selection to try and maintain the optimal perpendicular relationship. It will try and do the same thing with the transverse plane of the ski base.

Next post we talk the walk.
 
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#14
Quote:
Originally posted by David M:
nolo. No, I don't sail but I have a gift in the ability to see (visualise) forces. 

One small step for man – one giant step towards better skiing

Scenario: You have been given conscious control of your balance system. You are standing erect on a level surface with your feet aligned beside each other and your weight equally distributed between them. You are about to take a step forward to a new position on the ground in front of you.

Objective: To move forward and resume exactly the same posture you started the movement from.
Challenges: You are standing in a strong position of balance because you are well connected to the ground and your COG is in front of your ankle joint enabling the use of eccentric muscle contraction. You are about to relinquish this position and let your body fall forward. If you are to avoid a fall you must place the lead (swing) foot in precisely the correct a-p, m-l coordinates. As you move your COG forward the lead foot must adapt to the ground surface and absorb the energy of impact in the process. It must adapt to the surface 3 dimensionally and then transform itself into a dynamically rigid base capable of erecting a structural column with which to support your COG. Your COG is trailing the ankle joint as it approaches the lead foot. So you can not use eccentric contraction for balance. You have to find a way to get COG back where it was before you took this perilous step and resume the use of eccentric contraction.

Risks: If you fail to get everything perfect you could fall on your head and seriously injure or even kill yourself.

OK, we’ve talked the talk. Now it’s time to walk the walk. Try it and see what you can discover. Good luck.
 
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#15
Quote:
Originally posted by Ric B:
Well we're all related through skiing.

Maybe I didn't phrase that question right about speed and control. In a given muscle is naturaly easier to control speed of use in eccentric or concentric use? I read a little blip about this once stating that shortenng was easier to control than elongating. But I don't want to side track the conversation.

My question on how to get more work done earlier in the turn relates to Nolo's fall line to falline turn and whether we're utilizing our lenthening to engage the forces or setting up an anticipatory movement to wait for the forward movenent to engage our skis. To get the work done earlier I need to actively lenthen structuraly to engae the contact point and work the forces early in the turn. to me this speaks directly to your point of eccentric muscle work and being more skeletal. Help me out if I'm wrong here.

I'm gonna have to read this more than once. [img]smile.gif[/img]
 
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#16
Quote:
Originally posted by David M:
RicB
There are 2 answers and both are yes.

If you are consciously controlling a limb/joint movement you have probably have more control in concentric. But if the issue is balance then the balance system must be in control. Here with eccentric contraction controlled by the stretch reflex there is no contest. Eccentric wins hands down.

Answers to your other issues await in walking.
 
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#17
Quote:
Originally posted by David M:
Nolo
I don't know about which muscle fires or how, but when I walk I seem to be levering the COG forward from the first point of contact at the heel to the center of the foot, where I feel my weight passing through the talus to the foot. However, I experience this from the ground up as "pushing" me into balance. This is what I feel when I am skiing well, the sensation of the snow pushing me upright.
DM: Very good nolo. The ground is pushing right up into your gut somewhere isn’t it? You are describing what it should feel like if you are in EC with the SR. Note that nolo is not talking about consciously using any force to push back. When you are using EC your body is pushing back like crazy. But that is not what you feel. If you feel like you are pushing back with muscles you are probably using concentric contraction.

nolo: So I am guessing that the stretch reflex is how we get our balance on the new foot.
DM: It is what you get to not how you get there. It is the process of getting to it that it key.

Disski
I think you'll find that to be WALKING you must ALWAYS maintain at least 1 contact point. Otherwise it is running, skipping etc.
(LM where are you?)
DM: Agree.
ie walking is 2 points, 1 point, 2 points, 1 point
DM: Same thing in skiing: on hard pack 2 points in last 3rd of turn then 1 support point
running 1, 0,1,0,1,

RicB
But Disski, not all contact is created equal. Would you walk the same if you had everything to lose as you would if you had nothing to lose? 
DM: Every step in walking involves a potential forward fall
RB: And in my understanding contact does not necessarily mean having a meaningful connection.
DM: According to Newton’s Laws it must.

Milesb
The center of gravity appears to be pulled into a new position of balance by a combination of momentum and muscular action of the lead foot/leg. I'm unable to pin it down more specifically, sorry.
DM: A bit more detailed than that but you are basically right.
MS: On skis it is possible and desirable in most cases, to start a new turn with some/all weight on the "lead" foot. Because that foot does not need to be moved. Right?
DM: OK, think about this. At the end/start of the turn COG is over the downhill ski. The new outside foot (which is uphill) is leading – just like in walking. How do you get COG over that foot? Hint. You don’t pull the foot back although many ski pros describe it that way.

Thank you all for your input. I will make this all worthwhile. I promise. The key thing I was looking for in the last posting was to demonstrate how little awareness we have of the process we use every day – walking. I want to drive home the importance of understanding that every movement of your body in the walking process has a purpose. This will start to become obvious in coming posts. 

The key issue I will get to is that although we all seem to agree that connecting strongly with the ground is essential to balance and movement this can be a very tenuous proposition in skiing. As you will come see much of what is regarded as the wisdom of skiing as it relates to boot design and fitting and ski design precludes any possibility of your body making this essential connection. This factor more than any other has influenced ski instruction to become preoccupied with ‘looking right’ at the expense of skiing functionally right.
 
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#18
Quote:
Originally posted by David M:
In walking and skiing the first move from a standing start, whether a step or turn, is somewhat contrived. To initiate the first step the body bends forward from the hips. If the swing leg is the right leg the torso will shift slightly towards the left leg. These 2 movements allow a single limb to support the weight of the body while freeing the opposite limb to swing forward. If you try this combination of moves you will find that it initiates the swing movement. Although we are typically unaware of it, horizontal rotation of the pelvis is essential to walking, as is rotation of the spine. 

A parallelogram mechanism in the pelvis abducts (turns outward) the swing limb while equally adducting (turning inward) the support limb as the pelvis rotates horizontally. If it were not for this mechanism the feet would not track straight ahead. It is worth noting at this point that this mechanism is extremely important in ski posture as will be shown later. It should also be noted that the support limb side is always the strong side. For reasons I don’t understand articles on ski technique have started referring to the lead limb side (inside turn) as the strong side. This is physiologically impossible.

As the foot of the swing or lead limb progresses forward the heel of the foot of the support limb raises as COG moves past it. At the point where the heel of the foot of the lead limb makes contact with the ground the toes of the foot of the support limb are also in contact. This two-footed strategy helps to reinforce balance at this critical moment. Another clue here for skiing.

This is where things start to get interesting. When the swing limb first leaves the ground it is said to ‘unload’. An unloaded lower limb is very different from a loaded limb. When a limb unloads it releases the tension in its muscles and tonus as it is called drops to zero. The foot of the unloaded limb becomes a loose collection of bones and the knee has considerable laxity or looseness in its joint. These characteristics are necessary because in bipeds (that’s you and I) the COG is stacked over the base of support at the feet. This means that any energy resulting from the interaction with ground or reaction force at the feet will tend to ascend up the body. At contact the foot and knee must be loose to allow the limb to adapt to the terrain while at the same time absorbing the energy of impact.

Then normal orientation in space of the foot of an unloaded lead limb is with the sole of the foot turned inward, toward the center of the body. It is said to be 'supinated'. When the lead foot makes contact with the ground it makes contact on the outer or lateral aspect of the heel. At this point the rest of the foot is still in the air. The forward momentum of the COG drives the foot into plantarflexion forcing it into further contact. The contact process is called the adaptive phase. In this phase the foot sets up the process to integrate with the ground setting the stage for the lead foot to become the new base of support.

Before I go further we need to understand something of the nature of the force applied to the ground by the foot. A force applied by one physical body to another will have a center of force. In walking this is called the center of pressure or COP. In effect it is the net center of opposing forces; i.e. the force applied by the foot and the force applied back by the ground (GRF). COP has an anterior-posterior coordinate (front to back) and a medial-lateral coordinate (middle to outside). When plotted on the contact pattern of the foot it resembles the cross hairs of a gun site.

In the next post I will explain the different types of muscle activity that come into play as the foot adapts to the ground as well as the process by which COG is positioned so that eccentric contraction and the stretch reflex can be brought into play. This will serve as a good reference to understand the conditions required in order to use these mechanisms in skiing.
 
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#19
Quote:
Originally posted by David M:
a bit more.

The foot is comprised of 3 bow-like trusses. The 2 largest trusses share a common spine at the heel of the foot and extend on either side of the foot to the balls of the large and small toes respectively. The leg connects to the foot on the rear spine of these 2 trusses through bone called the talus. A third smaller truss extends across the balls of the large and small toes. A large sheet-like ligament called the plantar aponeurosis ties the 3 points of the arches together. In supporting the weight of the body these 3 points (heel, ball of the big toe, ball of the small toe) act as buttresses. 

When the foot is unloaded the bows of the arches relax, and in so doing, release the tension from the plantar aponeurosis. A reasonable analogy is an umbrella that is partially open. In this position the struts are loose and easily moveable in relation to each other. As the umbrella becomes fully open the struts apply tension to the cover of the umbrella rendering it more or less rigid when the process is complete. The foot undergoes a similar process as it adapts to the surface of the ground.

The tensioning of the arches of the foot could not happen without a key muscle in the back of the leg called the soleus. The tendon of the soleus wraps under the heel bone in a wide band on one end and extends to the top of the tibia (the shin bone) to a point just below the knee. What is important but not commonly recognized is that the fixation of the soleus at the heel integrates with the plantar aponeurosis in effect extending the soleus to the balls of the feet. The importance of this arrangement will become obvious when I discuss balance.

Continuing with the adaptation process as earlier stated the outside or lateral aspect of the heel bone contacts the ground first. As it does the foot begins to plantarflex or extend towards the ground. As this happens the soleus muscle passively shortens and a muscle running along the shin called the anterior tibialis goes into eccentric contraction. The role of the AT is to control the speed of plantarflexion and prevent foot slap. Those who overdo running come to know this muscle if they get shin splints.

The outer border or lateral aspect of the foot begins to make contact with the ground next. Remember that the unloaded lead foot is supinated and the sole is turned inward. This means that the lateral border of the foot will be lower than the inner aspect. As the foot contacts the ground the forces will reverse the supinated position of the foot and drive it towards pronation. This is a completely normal and essential process. As I will soon demonstrate ensuring that the adaptation process is permitted to fully occur is fundamental to balance with the use of the stretch reflex. 

More later.
 
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#20
Quote:
Originally posted by David M:
In my last post the lead foot had gone from being unloaded with its sole turned towards the centerline of the body to making contact with the ground. As the outer or lateral aspect of the foot made contact with the ground the weight of the body applied a force to the foot against what force? The ground reaction force, i.e. the force pushing back. The misalignment of forces has caused the foot to begin to rotate away from its supinated position into the direction of pronation. It is doing this because of the forces set up and not because of any conscious effort on the part of the person doing the walking. What we sense here is the ground pushing back. 

Now, let’s just think about this for a moment. In a skiing situation the foot would be turning away from the hill prior to contact with the snow. The forces of making contact would begin to drive the rotation of the foot into pronation (into the hill) simply as a result of our weight pushing the foot against the ground (read ‘snow’). Remember that this is the new outside leg of a turn here. Is anyone going to suggest that this a bad thing? 

If the ground were sloped across the line of travel so that the inner aspect of the foot made contact first then the forces set up would cause the foot to rotate even more in the direction of supination. Some would argue that this would certainly happen in skiing. True – unless a way can be found to make the outer aspect of the new foot contact the snow first. [I think nolo knows the answer to this issue] If we can start this movement then it would seem that we could drive the edge of the outside ski into the hill by doing nothing more than aligning our COG in the right place through our foot. And remember that the foot does not like working on a sloped surface. In view of this it would seem that if anything we would want to maximize the process of pronation rather than preventing it. Yet, the current wisdom in skiing is that pronation must be prevented at any cost.

Principle:
When the foot makes contact with a surface that provides a source of resistance (i.e. it pushes back) the foot will always rotate on its axis away from the border of the aspect of the foot that makes contact with the ground first. 

What mechanism makes all this possible? 
From The Physiology of the Joints:
“In fact, the ankle is only the most important of the joints of the posterior (rear) half of the foot. This series of joints (in the ankle complex), assisted by axial rotation of the knee, is in practice equivalent to a SINGLE JOINT with 3 degrees of freedom (anyone know what DoF means?); it allows the foot to take up any position in space and adapt to any irregularities of the ground.”

Question: If the series of joints that make up the ankle and the knee joint all work together in concert so they act as a single joint why are strenuous efforts being made to isolate certain joint actions at the exclusion of others. This is precisely what ski boots and many forms of footbeds and custom fitting attempt to do. 

More on walking coming soon.
 
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#21
Quote:
Originally posted by Ric B:
DM, your exlpanation of the biomechanics of the foot is right on with my basic understanding of the foot. I'm with you on the contact of the little toe side of the foot first in starting a new turn, and I do believe like you that it "can" done through a simple alignment of the COG over the new outside foot, really this is what makes this foot the new outside foot. I'm with you all the way to axial rotation of the knee. My understanding is that the knee can rotate around an axis, but it doesn't rotate itself, it's a hinge joint. For the knee to rotate around an axis, the hip socket needs to be activated. Is this what you meant? Continuing on with my understanding, this rotation of the hip coupled with the pelvic tilt you spoke of in walkng, combined may be used to control alignment of the COG and thus create that contact point on the foot needed to the desirable sequence you speak of. Please correct me if I'm off track. And please keep going, but don't take away my footbeds. [img]tongue.gif[/img]
 
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#22
Quote:
Originally posted by David M:
I am goint to use nolo's quote to make a point.

nolo: "Who says to pull the new outside foot back? I have heard of holding back the inside foot from getting too much lead to maintain pressure on the center of the outside ski and to aid in tipping the inside ski to the outside edge for refined steering."

There are probably some out there who are thinking that my intent is to make skiing more complicated by having the skier think about a whole bunch of things. In fact my intent is to have you think about as little as possible. Thinking about pulling the foot back or tipping the ski on edge is way too much information when you are going 40-50 feet per second. Worse, it screws up your balance. In complex actitvities you get control by giving up control to your balance system. Reflex actions are tens of time faster than consciously mediated actions. 

Instead of tensing you have to work on learning the right position to turn on the stretch reflex and then relaxing. Less is more. For some reason females seem to get this easier than males. Just watch female golfers. They don't try to kill the ball.

If you really want to experience the huge rush of skiing you have to provide an environment where the balance system is in complete control and knows this. This is the only way to avoid the high anxiety signals that tell your body it about to die.

....
 
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#23
Quote:
Originally posted by David M:
RB: “……good skiing is having no movements left to get rid of”. 
DM: Agree completely.
RB: Which to me means that we are using the least amount of energy to move our mass the same distance, because we are not marking counteracting movements that aren't required”.
DM: Let me put it another way. We are letting the forces acting on us do as much work as possible by using them to our advantage instead of fighting them.
RB: This leads me to reducing the starting and stopping of my movements. Making my movements more fluid. 
DM: YES!
RB: It would seem that if I'm constantly starting and stopping I'm using energy that's not needed. Too much concentric muscle action? 
DM: Confidence is high of this conclusion.
RB: DM, we played with hip lift and resulting rotation on the snow without skis, but in our boots last year with an examiner. The focus being on how this lifting of the hip in skiing allowed the release of the stance ski and allowed movement down the hill. There was a natural rotation of the hip and empty leg forward when done without skis. 
DM: I am just about to go there in the next couple of posts.

..!
 
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#24
Quote:
Originally posted by David M:
DM: The forward momentum of the COG drives the foot into plantarflexion forcing it into further contact. The contact process is called the adaptive phase. In this phase the foot sets up the process to integrate with the ground setting the stage for the lead foot to become the new base of support.

nolo: Does the foregoing mean that as we release the inside edge of the stance ski, we (simultaneously) initially load the outside edge of the new stance ski and (extend the leg to push against the momentum of) the (falling) COG (to) drive the foot into plantar flexion? Is the skier bowlegged for a split second there? DM: No because we are moving downhill as a unit.

DM: You're good nolo! The answer is yes. But I am referring to walking on a continuous hard flat surface. Let me get throught the cycle then I will take it to skiing where inportant aspects of walking are the same but the physics are different. In skiing we have to make different moves to help kick start the process.

Please hold the questions until I get through the details of walking. We are just about to the really good stuff.
 
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#25
Quote:
Originally posted by David M:
nolo: Okay, David. Here's my answer. We need the GRF to lever the COG over the talus in order for the weight of the skier to pass through the ankle joint to compress the foot into plantar flexion. 
DM: How about dorsi flexion? What muscle kicks in to stop dorsi flexion. What would you do if you wanted to increase dorsi flexion?

nolo: The resistance of the inside front of the boot enables us to extend with the quads and tibialis anterior, which are the two extensors in the lower body (lower limbs). The extension enables the stretch reflex to occur. 
DM: You are absolutely right here when you suggest that skiers use the stiffness of the boot shell as a source of resistance (i.e. reaction force) with which to apply muscle effort. But this becomes necessary when the boot messes up the normal systems which are far more effective and efficient. It is the forward momentum of COG created by the extension of the (old) outside leg that allows the quads to kick in and get COG over top of and ahead of the ankle to make what possible?………………eccentric contraction. What muscle is the most important muscle in posture and balance at this stage? 

RicB
Unweighted flex of my ski boot is coming just about entirely from the muscle running up the front of my shin. I believe this is the Anterior tibulas if my memory serves me right.
DM: AT and others. How much could you flex the boot with muscle effort alone? How about the weighted flex? Did you experience any difference between the 2 types.

RB: So DM, we need some small amount of room in our lower shell. I'll say this from my personal experience, I like lots of toe room, with no room over my instep and a tight fit around the heel. 
DM: Good so far. Just be careful about how tight you make the heel and where you make it tight. Getting this right is important. 

RB: The booster strap adds to the movement with contact. That progressive flex. And that's where I see you going with this "conducive environment". 
DM: There are some very important issues relating to ‘progressive flex’ that I will get to. This is a hypercritical issue in terms of balance.

FOOTBEDS
This is a huge and very contentious issue in skiing. I was one of the 1st to make and promote the hell out of footbeds back in the late ‘70s. I used to tell skiers “Don’t leave home without them”. I was the footbed God in our whole area. Most of the time the beds I made seemed to do some thing positive. Sometimes they made things worse. There are a few important issues here.

- Skis geometry with 70 mm waists did not facilitate the use of the normal balance responses, and
- There are 3 types of arch structures; tight (doesn’t change much under load), moderate and loose. What I found was that most good skiers of that day had tight arch structures. This is an advantage if the boot is not that conducive but not so much of a factor if the boot is right. If you have a loose arch structure (as I have) then you need a boot God to help you ski.

RB: My Atomic has the toebox slightly skewed to the outside. From the conversation here i'm gonna say that that could be a good thing if the fit is good. 
DM: Wait for more material from me. Then you can decide.

RB: It's the best skiing boot I've ever owned, at least for me. Where I'm hoping you will go with this is to help us determine what we can do to find the best fit, or that "conducive environment" within the existing boot selections.
DM: RicB we are about to go where no man has gone before-- to the reaches of the universe. “All ahead warp speed Scotty”.
 
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#26
The reason our body eventually learns an activity like skiing has to do with survival. Until very recent times in the continuum survival has been inseparably linked to mobility. If you couldn’t run you got killed and/or eaten.

When we clamp a device like a ski boot on our feet and then persistently expose our bodies to danger it has no choice but to adapt. The fact that skiing keeps coming into the picture sends a message to our brain that this activity is somehow important to survival. And so it adapts any way it can. We eventually do learn to go down the hill. 

What needs to be recognized (and it hasn’t been to date) is that if the ski boot seriously impacts our normal processes, especially the process of balance, then it is in reality an external quasi - pathology grafted onto our body. What is the difference between an ankle that has been seriously injured and is now fused at its joints after healing and essentially non-functional (again an example of an adaptive response)and one encased in a ski boot? Not much. In the food chain we are now the food.

What are the implications of the preceding? When we fail to provide an environment conducive to good function and then continuously expose our bodies to danger we begin a process that causes the body to reassign its hierarchy in terms of protection against injury for things like stress radiating up the lower limbs from the ground or snow surface. When we do this the body tries to absorb potentially injurious energy in other less effective ways. But over time it eventually begins to accept a higher risk of injury as unavoidable in order to survive. 

Given the above when we promote an activity such as skiing we need to recognize the potential consequences and to take steps to ensure that equipment and ski teaching does not amount to a process of adaptive training wherein the body will modify its priorities in a manner that dramatically increases the risk of injury.
[/quote]
 
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#27
Quote:
Originally posted by nolo:
Quick question, David. Is this a true statement?

The ankle joint doesn't really extend or flex. Generally the terms plantar flexion mean flexion and dorsiflexion mean extension.

??? I am confused because plantar flexion seems to open the joint and dorsiflexion seems to close the joint. 

Your question to me was: How about dorsi flexion? What muscle kicks in to stop dorsi flexion. What would you do if you wanted to increase dorsi flexion?

Dorsiflexors are the muscles of the anterior leg. I would posit that the tibialis posterior kicks in to stop dorsiflexion. If I want to increase dorsiflexion I would pull my toes toward my knee.
 
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#28
Quote:
Originally posted by David M:
Ok nolo I know I am probably slowing driving you insane. So I will give you a bit of help. Just realize that I want you to learn. You are obviously intelligent. But at the same time I have to acknowledge these are tough issues.

First 'ankle' means 'angle' (in Latin I think). Next human locomotion given all the issues associated with bipedalism presented tough problems. Who or whatever created us had to find a simple solution to walking and balance. They did. They put all the major muscles of the leg in the back. 

If we swung from the trees at one time foot flexors were probably more important than they are now. So the first thing you have to consider is that the soleus in the back of the leg produces plantarflexion (extension) in both weighted and unweighted function. 

Weight bearing is very different than the unloaded state because in weight bearing gravity is trying to disturb our upright posture. This required a simple solutiuon that would produce predictable results. The soleus intervenes to oppose the force of gravity tyhat is trying to cause us to fall on our face. What it if it stopped contracting altogether? You are literally standing on the answer. :
 
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#29
Quote:
Originally posted by nolo:
Another note: I'm sure we all want to know if "our boot" is one that creates a conducive environment. We spent a week's or a month's salary on them and we had planned on keeping them for a couple of years at least. 

I'm sure the long-timers on the site are sick to death of me raving about my boots, but I feel the same as Ric about my boots. I was in a Tecnica TNT and then the Icon-8 before I switched to the Dolomite Sintesi junior race boot. My skiing shot through the roof with that one equipment change. Suddenly I had all sorts of feel for the snow and I felt extremely mobile in the lower leg/ankle/foot. At first I thought they were too soft and mushy, me being used to the higher, firmer men's Tecnica (sized way down, thus stiffer, I believe), but then my body started adapting to the new situation by lining my COG over the ankle instead a bit forward, levering on the front of the boot. Now I feel I get my leverage from the ground. I feel thoroughly stable all the time (barring a full moon). The feature I particularly like is the fifth buckle that keeps the heel in the pocket. Being a typical pie-footed female, I have a narrow heel and a wide instep. I also have a London Bridge foot, and I love my Peterson footbeds that I've had since 1987. This boot fits perfectly. I put them on in the morning and I take them off at the end of the day, as I would a pair of shoes.

Anyway, I feel my boot is a conducive environment for good skiing. I definitely hear you when you say that most boots are not, and I feel that women have gotten a bum deal having to wear a man's last until just recently. Hot women skiers designed K2's T9 Series of incredibly great skis for any sex (disclaimer: you know who I work for). I dream of the day that real women skiers can design a boot for women (though Dolomite came through with the junior boot and for that I thank them). I also believe that any boot is going to require a bit of work to fit it properly.

But the group that I think gets the real short end of the stick are intermediates. I blame the boots for the backseat stance.
 
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#30
Quote:
Originally posted by David M:
...
nolo: Re extension and plantarflexion etc. A few years ago a biomechanics society tried to sort out the confusion. Yes, technical terms are all over the map. Normally extension means to extend the angle of the joint. But some disciplines seem to stand on their heads so the world is upside down. For this reason I prefer that the group create their own language. So long as it works I will agree to anything.

Your comments on boots are consistent with my experience. Boots for females always have and probably will be for some time based on men's shells. I will get to the reasons for this soon.

Meantime the flex answer has not emerged. So I am going to tell you the answer. You flex your boot by releasing contraction of the soleus. The force of gravity levers the cuff with the free hinging tibia by pulling COG downward.

If you read through my previous material you will note that I said the soleus was the single most important muscle in balance. I add to that and say "balance and foot function".

Is it a good thing to release the contraction of this muscle at any time, skiing or just plain standing. Any takers?
post #3 of 28
Thread Starter 

SECTION 2

 

 

 

Quote:
Originally posted by David M:
Back to the conducive environment issue. 

Keep in mind that I did research with an instrumented device back in 1991 that allowed our team to acquire 3 D data on foot and leg pressures while skiing and compare this data with video and subjective skier input. Sofar as I know this has not been done by anyone else even today.

In some instances good skiers learned for the first what they were doing when they saw the data and video. It was often very different from what they thought they were doing. In addition, when they studied the data they always agreed with it. Keep this in mind. If I were to do the same thing with any one of you out there I would expect to get the same disconnect with reality. This is the main reason good skiers can't tell others what they are doing. Any explanation they try to give is usually miles from reality. It is also why they believe skiing is easy. For them it is. For the same reason such skiers ‘don’t get’ discussion threads such as this.

Otto: When Gleason in Taos asked me to come in and let him excavate my boots the other bootfitters stood around and marveled at what I did with an Exacto knife, heat gun, duct tape, pieces from my previous boots and chewing gum. After he got through with fitting my boots they fit just as before, only with a lot fewer pieces. I don't unbuckle or take them off all day either, why should I?
DM: Sounds like me at work. Most of the crap in ski boots does nothing but cause problems. I used to horrify boot fitters at my technical seminars with what I did to brand new boots. They just could not bring themselves to do the same thing for their customers. They tended to believe it was merely a matter of finding the right boot. Yeah right! I used to log 15 to 30 hours prepping a good pair of boots for a WC racer. And yes, you should not have to unbuckle them. In fact it is better not to.

Otto: One of the first things I do with all my boots is modify the forward flexibility to give me a range of mobility without putting tongue pressure on right away, that allows me to be in variable forward/aft positions, as in bump absorption, etc. without affecting the skis, unless I want to.
DM: If you are saying you want free space in the cuff to allow for ankle/shin movement before you begin to compress the tongue then I agree. This is absolutely essential. The worst thing you can do is to cinch the cuff around your leg to as the saying goes “transfer energy”. You will certainly do this -- right to your knee, hip and back.

Forward Lean
If you are also saying that you take some forward lean out of the cuff then we may be related. In the majority of cases boots have way too much forward lean for the angles of the joints essential for postural responses driven by the stretch reflex. If this is indeed the case you don’t have less stretch reflex you have none. The best way to tell if a skier is using the stretch reflex is to watch them ski through crappy rough snow, the kind the usually tosses skiers all over the place. If they look like they are skiing groomed hardpack they are probably using the SR.

Liners
Liners can and often do cause more problems than boot shells. The Lange World Cup liners with flow packs I can rip out in 2 seconds are my favorites. My wife’s boots are Head shells with lots of modification with Lange liners and a Dachstein tongue. What is the best way to fit most liners?? In the garbage can.

.
 
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#32
Quote:
Originally posted by David M:
...Here is where we are at so far. The boot lower shell or tub as I call it has to provide adequate 3D space for your foot to function within under the maximal skiing loads. Interestingly lack of forefoot width was a big problem in footwear like running shoes until companies like Addidas began to fund research to see how wide the forefoot was just prior to propulsion. The guy who did the research at the Human Performance Lab in Calgary now lives in Whistler. I have copies of his papers that give the required width for various shoe sizes. Traditional 'lasts' as they are called were way too narrow. If you saw these lasts you would know why the ski industry is in the dark ages. 

When I compared the loaded width requirements to the widths of typical ski boots a size 9 boot shell (without the liner) was about 1 cm too narrow (that's about 1/2 inch for you Americans). Not bad you say. Actually, it is very bad. The liner is about 1/2 inch thick. Now we are too narrow by 1 inch for an average width men's size 9. Imagine the situation for a wide forefoot. There is no way your foot can function with this constraint. This is not open to debate.

What if the boot is wide enough in the forefoot but does not provide enough clearance for the inner ankle bone and bones of the midfoot? 
In this case the inner aspect of the foot hangs up preventing the sole from 'touching down' on the boot base. Sure some of you can still ski but it takes brute strength because you can only use concentric muscle contraction. What you may not realise or accept is that your foot is still trying to adapt to the terrain. It has not developed the tension and balance it needs in its truss like arch structure to set up the buttresses requied for the muscles of the foot and keg to pull against in a COORDINATED manner. 

Force applied to the foot by COG acts on the downhill side of the inside edge of the outside ski. Anyone good at mechanics and physics in the group should know this is not a good thing. In such situations saying "watch me ski" doesn't impress me. You are driving a delapidated wreck of a car.
 
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#33
Quote:
Originally posted by David M:
Ott: There is a story in the premium section in which I desribed my first ski boots in 1944. I went to the shoemaker, he stood me on some cardboard and traced my feet, took some wooden lasts off the wall, measured and eyeballed and when the boots were ready they fit like a glove, or shoe.

In the 56 years since, wearing many, many different boots, I never rested until I got a fit that, dancing the polka at the tea dance after coming off the mountain, I felt no need to unbuckle.

DM: The reason skiers like Ott "just ski" is because they can. From the very first time they skied they had a conducive environment for function. It may not have been perfect but it was good enough to ski in. Ott had 'been there' in terms of this environment long before he clamped his feet in hard shell stiff plastic boots. Once he had been there he knew what a conducive environment should feel like. Ski boots that are the most comfortable shoes you can wear.

The problem with skiers today is that they have never been where those such as Ott have been. They have no clue as to what a boot should feel like. They have to learn this after the fact.

I am confident that I can alter a ski boot so that even God himself would ski so badly as to make a rank beginner look like a World Cup star. And there is nothing he would be able to do about it.
 
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#34
Quote:
Originally posted by David M:
If you go back and read my earlier discussion on the events of walking you will note that after the triad of arches of the foot have made full contact with ground the ankle switches from plantarflexion to dorsiflexion. This movement begins to stretch the soleus muscle. What happens next represents one of the most critical events in both walking and the transition to an upright posture. As the head of the tibia passes in front of the ankle the soleus switches to isometric contraction. It stops lengthening and arrests further dorsiflexion. If it were not for this event three things would result; 1) the truss-like arches of the foot could not be tensioned by COG exerting a downward force to compress them, 2) the knee could not extend to lever COG up and over the ankle joint to arrive in front of it and, 2) the body would fall over. 

The most important function of the soleus in arresting dorsiflexion is that the foot needs this to happen to become structurally competent in order to support COG. The balance system needs the arches to become tensioned before they can act as a proprioceptive receiver for critical information pertaining to balance. In short the foot needs the soleus in order to function period. 

In addition the angle of ankle joint at which dorsiflexion is arrested is critical to the use of eccentric contraction in the chain of muscles that extends form the heel of the feet (or foot) to the pelvic girdle. If the angle of dorsiflexion of the ankle is too great the COG can not be levered over the ankle since it would have to move too far forward for the eccentric contraction of the gastroc to arrest it. The result is that we stay erect by squatting. 

What are the implications for the ski boot? The angle of the cuff or shaft of the boot has to be compatible with the critical angle at which the soleus switches to isometric contraction. This should be the angle where the calf of the leg rests against the rear cuff of the boot. In a small percentage of skiers the boot shaft may be compatible with this angle. In most cases it is far too great. Rarely is it too straight.

The reasons for excessive forward lean are numerous. First and foremost is that the current wisdom in the industry is that this amount of forward lean is essential to skiing. This fit with the paradigm that pressure can be effectively applied to the fore body of the ski by the skier applying force to the front to the cuff with their shin. While this is true the physiologic consequences are severe. 

The only possible way significant force can be applied to the front of the cuff by the shin bone is through the release of contraction in the soleus. This has two immediate consequences; 1) the foot becomes non-functional and the soleus can no longer sustain isometric or eccentric contraction. The effect is as if the skier has suddenly become disconnected from the ground from the knee down. Far more serious is that the tibia is now unprotected in the event of a forward fall. When in eccentric contraction the soleus contraction in well positioned to intervene to oppose stress on the tibia. This is no longer possible.

The mechanics work like this. The soleus relaxes allowing the weight of COG to act downward on the tibia. This forces it to dorsiflex against the cuff. There are 2 components of force here. One presses down and is resisted by the ground. The other acts horizontally towards the front of the boot. The reaction is down and back where it is resisted by the heel of the skier. As the cuff is progressively flexed pressure applied by the foot to the sole of the front of the boot decreases until the only force applied by the foot is under the heel. In effect the forefoot is now 'floating' about the ankle joint.

After the shin strikes the cuff and compresses the padding it starts to bend the shaft forward. This actions sustains the relaxation of the soleus muscle. How? Gravity normally acts to pull COG forward (i.e. dorsiflex the ankle). The soleus pulls back in the opposite direction (i.e. it plantar flexes the ankle). This is the normal balance equation where an internal force opposes an external force. Using the shin to flex he boot adds a new external force, the force in the bending resistance of the boot cuff. This third force has one very serious problem. It is on the wrong side of the equation. Think about this. Do the math.

I’ll be back.
 
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#35
Quote:
Originally posted by David M:
Boot flex continued

Balance results when 2 equal and opposite forces are aligned in opposition to each other on a common path or vector. 

In skiing a vertical force or a quasi-vertical force (i.e. behavioral vertical) pulls the skier down and the skier uses GRF to generate an opposing force with which to push back. The skier is in balance when the sum of all moments of force acting across the joints of the ankle complex and ascending upward through the knee at any given time equal zero. In the equation an internally generated force (i.e. muscularly generated) opposes an external force that tends to disrupt the skier’s equilibrium. The resulting equation looks like this:

1. F internal = F external

Since rotation of joints is the key issue in this balance equation the opposing forces can be thought of as clockwise and counter clockwise rotation. If in the external force is trying to rotate the ankle clockwise (into dorsiflexion) within the physical reference then soleus will oppose this force by rotating the ankle counterclockwise (into plantarflexion). 

If the bending resistance of the cuff or shaft of the ski boot is opposing dorsiflexion of the ankle what direction is it acting? Counterclockwise. Therefore it is aligned in concert with the soleus. Now the equation looks like this:

2. F internal (muscle) + F2 external (ski boot) = F1 external 

If you compare equation 1 with equation 2 you get:

1. F internal = 2. F internal (muscle) + F2 external (ski boot)

Therefore 1. F internal – 2. F internal = F2 external (ski boot)

CONCLUSION: Adding the bending resistance of the boot shaft into the equation forces the soleus to reduce its level of contraction. 

Is this a good thing? We will see in my next post.
 
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#36
Quote:
Originally posted by Lisamarie:
VOILA! 

Scroll down, there are a few charts of the lower leg. Even though I do not see any copyright info, we better cover our a$$es and just put up the link. Besides, there are way too many pictures. A suggestion: If you want to refer to a specific picture, copy and paste the url of that picture. That way we will be scrolling less.

.
 
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#37
Quote:
Originally posted by David M:
If someone wants to start a new thread it is fine with me. So long as we keep the perspective that all the segments relate to balance.

More boot flex/forward lean issues

There is one more interesting effect related to boot flex. When COG is supported on the base of support at your feet the weight is carried under the heel and the balls of the feet (COP is the center of the pressure or weight). In terms of balance the base of support under your feet is what your balance system uses to help determine which way is up.

As explained in my last post when the soleus is relaxed and the shin begins to bend the cuff the pressure under the forefoot decreases until it is only under the heel bone. As this happens the plane of reference for the balance system switches from being the plane defined by the heel and the balls of the feet to a plane defined by the heel and the center of pressure (force) of the shin on the cuff. (You connect the 2 points with a line to find the plane of reference). To the balance system it is as if the ground suddenly tilted up from level to 45 degrees. 

If you have too much forward lean in your boots and you hit a bump or mogul and your shin suddenly loads the cuff will this panic the balance system? Of course. Will you pitch forward wildly at the waist in response? Probably. Any females out there with moderate to large calves? Do you have too much forward lean in your boots? Odds are that you do. Did you recognize the sensation I just described. Yes? OK, it wasn’t you. It was your boots.

So, why do ski boots have the forward lean angle they do? The first reason is because they have to look good. And boots don’t look nearly as good if the cuffs are straighter. The second reason is that someone has decided that you need this lean angle to put pressure on the front of the ski. So, we have that, what do they call it…….., oh yes that “aggressive forward lean”. We’ve already sunk that theory. 

What determines individual forward lean requirements? First and foremost is the critical angle at which your ankle joint switches to isometric contraction. This angle should be shaft angle or lean of the boot where your calf rests against the rear cuff. You need some free space to flex forward from here. We will get into this later.

What determines the lean angle of the shaft of the boot? Manufacturing considerations. Remember that the boot maker has to have an economical way to make a boot. No matter what angle he choses the boot maker has to fix the cuff to the lower shell so the two components act as one. At this point the boot is a bent plastic tube with a seam up the middle starting at the toe so you can bend the flaps open to get in. 

But, doesn’t that big rivet on the side of the cuff allow it to hinge? I think not. The resulting plastic structure would not be stable enough. Here’s a bit of trivia. The stiffest plastic you can make a boot out of that won’t break like glass in the cold is about 1/20th as stiff as steel. Plastic boots generally rely on wrapping tightly around your foot for their stability.

There has been some inference in posts by others that I believe boots should be soft. I never said that. Did I say that? No. If a boot is set up right I believe they need to be very stiff on the sides of the leg but not to apply leverage to the ski edge. This is one of those external force on the wrong side of the balance equation issues. The shaft of the boot has to be stiff to provide a stable vertical reference to help you align internal forces through your foot. It is like training wheels for your balance system.

The process by which the boot maker establishes and fixes forward lean is at best arbitrary. It can be all over the map from one boot to another. 

The big problem for the skier is that the forward lean of the boot is decided behind your leg where the calf muscle is. The forward lean angle you require for skiing is determined by the angle your shin is at when the soleus switches from eccentric to isometric contraction – i.e. the critical angle. However the ski boot typically over rules your body because the rear cuff will push your shin forward based on what? Based on the size of your calf muscle where the boot cuff wraps around it. 

What does this all mean? Well if you have a large calf muscle you are in big trouble. If standing up for more than 5 minutes is exhausting do you think there is any hope you can ski? Not likely. Even if you have a small calf you may still be in trouble if you have small feet. Why? Because although boot makers allow for some variation as they shrink shell sizes down they still use the same forward lean angle on the cuff. Why? Looks, looks. The boot has to look good. Looks aside the other reason is “because that’s what we do”. In other words, “don’t ask us”.

Is forward lean easy to change. Sometimes. More often than not it can be a nightmare. The reason for this is that the molded interfaces can make it very difficult to put the cuff at an angle that is much different than the boot maker designed it to be at. In many instances I have not been able to straighten the shaft enough. A brand new pair of boots I bought for my wife 2 years ago went into the garbage because I could not make them upright enough for her calf.

One more issue. Assuming you can successfully align the cuff the next nightmare is the liner. Remember, it was formed to the shape of the shell the way it came from the factory. Am I saying forward lean can be a tough problem to correct. Absolutely.

This pretty much wraps up the boot flex issue. Please post any questions you have on this issue before I move on. Thanks
 
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#38
Apologies in advance in case anyone is offended at my cut & paste job
 
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#39
What an effort Disski. I actually put all the rellevent posts into word yesterday for my own reference and study. Thanks a bunch. [img]graemlins/thumbsup.gif[/img]
 
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#40
RicB 

A bit about my experiments of 1991. The device that replaced the ski boot was a minimalist aluminum frame instrumented with 18 force sensors strategically placed so as to obtain 3 dimensional data on the forces being applied by the foot and leg. The device had provision to apply localized effects to specific aspects of the foot and leg in order to study their effect. For example, plates on either side of the balls of the foot could be repositioned to prevent the foot from spreading fully under load or to reorient the foot across the long axis of the ski (i.e. to turn the forefoot outward or inward).

Relevant to the present thread is that the cuff of the boot rotated about an axis. The cuff could be adjusted around the skier’s leg so that there was no front to back slack. This was done without compressing the calf muscle (although we could certainly do this too). 

The forward lean position of the cuff could be adjusted with a backstop. The degrees through which the cuff could rotate with essentially zero resistance was adjusted once the forward lean was set. We could also allow the cuff to be completely free hinging in that it could rotate all the way back until it was almost horizontal as well as rotate forward well beyond the normal range of motion of the ankle. The device had provision to permit various forms of resistance to be introduced at the end of the free play. We could also vary the constraint that would prevent the midfoot from articulating properly. One very important feature was the neither anklebone would ever be impeded in its horizontal transverse movement. 

The results of the experiments were enlightening. What we found was that by varying the constraints of the cuff function we could play the soleus muscle like a musical instrument. For example when we set the forward lean too upright we would witness multiple attempts by the balance system to get COG over the top and ahead of the ankle. But the most amazing thing we did was to have skiers attempt to ski with the cuff completely free hinging. When a skier suggested this I thought he had gone insane. I was proven wrong when suddenly he was skiing beautifully right before my eyes. 

Most interesting of all was that the tech guy (a biomedical engineer) monitoring the incoming data was set up in a tent and could not see the ski hill or the skier. Although he was not a skier he was giving us very accurate information within a day as to how well the test skiers were skiing just by looking at the incoming pressure data -- no video that was added later! This completely blew me away.

Once I figure out how to import drawings I will try and put a picture of “The Gadget” as I named it.

One thing to note is that experiments on the effects of footwear done at the Human Performance Lab in Calgary, Alberta have shown that when constrained in footwear the human foot will always begin by trying to create its barefoot function. It will then negotiate an increasingly compromised solution until it has found the level where it can work within the frame of reference. This is in essence what we were researching with our experiments.
 
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#41
What David is saying rings a bell. When I was in the men's boots I definitely was in dorsiflexion at turn's end: 1) stiff race boot, sized down; 2) high boot, large calves; 3) the aggro forward lean was adjustable, the rear spoiler removable, but the boot shaft was strangling my calves, causing my feet to fall asleep on the chair, and I needed to install boot heaters to keep my formerly severely frostbitten toes alive. In the junior Dolomite Sintesi, I have not felt the need to heat the boots ever, with only dance tights on my feet. This alone improved my performance. How can you ski with numb feet? 

I was a woman in mortal combat with her boots. No wonder women drop out at a higher rate than men. How do I know that? The statistics tell me so.

[ November 25, 2002, 07:17 AM: Message edited by: nolo ]
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#42
disski has done a great job, and all of you are amazing! What a phenomenal thread! Should this be put into such form that it can go into the "Premium Article Collection"?
 
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#43
With me also Nolo. I hate to wear out the Tai-Chi connection, but the structural awareness I got working through grounding my COG and maintaining my balance in movement through the forms by focusing on developing my root, or full foot contact, and everything working up from that point plays right into this discution. How my newest boots allow a better feeling of being connected at the foot, by allowing more natural movements. Just can't wait to get out on the snow.

Nolo, I liked how you expanded Horsts's qoute in the other thread. This is all about teaching as far as I can see.

DM, Thanks, and keep going.
 
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#44
Quote:
Originally posted by David M:
Here is something to think about while you are waiting for my next post on walking. 

The foot has 3 loading bearing points situated at the lower ends of its bow-like trusses: the heel bone (the calcaneus), the ball of the big toe (the head of the 1st metatarsal) and the ball of the small or 5th toe (the head of the 5th metatarsal). They represent the mechanical references of the foot. 

In skiing the ball of the big toe is the most important of the 3 mechanical references because it represents the furthermost point into the center of a turn from the center of the outside ski that the foot can apply force. Under the right circumstances and with a functional foot COP can be driven to the ball of the big toe. 

NOTE: A functional foot in the above context is a foot capable of loading the ball of the foot by levering the 1st metatarsal. 

The current theory is that edge control results when the force applied by the foot somehow aligns itself over the inside edge of the outside ski. To date no one has explained the mechanism by which this alignment takes place. This issue aside, the theory is flawed in itself because it ignores the effect of sidecut. 

The sidecut of a ski effectively increases the width of the ski as measured at the waist. Therefor an alignment of the force applied by the foot with the edge of the ski at its waist would still result in a misalignment of opposing forces. This will cause the foot to move into supination or away from an edge set. Even if the theory were valid it would still not produce a stable base of support which is essential to initiate movement from. According to Newton’s Laws “for every action there must be and equal and opposite reaction”. You can only push as hard as the snow pushes back. If the base you are pushing against shifts you will lose the balance equation because balance results from the alignment along the same vector path of 2 opposing forces.

Does anyone know the solution to this problem?

..?
 
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#45
Disski, You absolutely rule for doing this! Thank you. The thread becomes much more coherent in this format. Appreciate it.

DM, a question, where in the process of transferring the stability of your balance structure to the shin and heel does support for the rear of the knee become critically compromised by the soleus needing to become less active in the balance process? Is this a progressive, or an on/off type of loss of support. Is the entire knee compromised or just specific directions. Is the point where the soleus turns on and off during walking and flexion the same point as when it is placed in a 'correctly' fitting boot or does the boot change the point. Thanks for your knowledge and time.

joel
 
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#46
David, I have a couple of questions.

1. What are the drawbacks (performance and safety) to using boots designed to your criteria?

2. Have you done similiar research on snowboarding?
 
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#47
Quote:
Originally posted by David M:
In my last post the heel and the outer (small toe) aspect of the lead foot had made contact the ground. At this point the foot had been plantarflexing (pushing down like pushing on the gas pedal of a car) to drive the foot into compliance with the ground. As the lead foot swung forward the pelvis began to rotate horizontally about the support leg. If the lead leg were the right leg and you were looking down on the pelvis it would be rotating counterclockwise. This means that the pelvis would be rotated or adducted into the support leg and it would be rotated out of or abducted from the swing leg. This is consistent with the fact that the support leg will be in a pronated position at the start of the walking movement while the unloaded lead leg will be in a supinated position. As the heel of the foot made contact with the ground the anterior tibialis on the shin had gone into eccentric contraction while the soleus was being passively shortened. 

When the heel of the foot made contact with the ground it established COP. COP then radiated along the outer (little toe) aspect of the foot as it made contact with the ground. On top of all this the foot has begun to reverse its supinated position and rotate in the direction of pronation. Something else important has happened. Walking is a forward fall. As the lead leg swung forward COG began to move forward and downward from its start position.

Does everyone have a good picture of this? OK. Here is where things start to get interesting. As the outer aspect of the foot comes into full contact with the ground the transverse aspect at the balls of the feet is also beginning to make contact. As it does COP swings across the foot from its outer aspect and begins to head towards the ball of the big toe. As the forefoot (balls of the feet) comes into full contact with the ground the ankle joint reverses direction and the foot starts to dorsiflex (i.e. pull up). As it does it begins to stretch the soleus muscle in the back of the leg causing it to go into eccentric contraction.

Something else is happening. Since the adapting foot is now pronating the pelvis is beginning to rotate about the adapting foot. As it does the side of the body with the adaptive foot is becoming the strong side because the pelvis is turning into the leg (it is becoming adducted). While this action has been unfolding the leg has been dorsiflexing with the soleus in eccentric contraction. As the knee passes over top of the ankle the soleus switches gears and goes from eccentric contraction to isometric contraction (i.e. muscle does not change length). I other words, it stops the dorsiflexion of the ankle dead in its tracks. Why?

Nolo: I don't know about which muscle fires or how, but when I walk I seem to be levering the COG forward from the first point of contact at the heel to the center of the foot, where I feel my weight passing through the talus to the foot. 

The body needs to get COG back where it started – in front of the ankle joint. It also needs to get the leg back into eccentric contraction. Think about what would happen if the ankle didn’t stop dorsiflexing. COG would keep dropping. It is already below the height it started from. As nolo said it has to be levered back up somehow. It does this by stopping the leg from moving and then pulling COG up and over the ankle by using the quads in the front of the thigh in concentric contraction. Once COG has gone over the top and is in front of the ankle the gastrocnemius in the back of the leg begins to be stretched by the extension of the knee joint. This causes it to go into eccentric contraction. Now COG is back where it started.

The action just described is fundamental to effective skiing. What is especially important is the angle of the ankle joint that is present when the soleus changes to isometric contraction. If our ski posture is set up correctly (I will get to this) the forces of skiing will cause the soleus to revert to eccentric contraction in order to maintain this critical angle. Am I suggesting that consciously ‘flexing your ankle’ in skiing is a bad idea. Absolutely.

If you walk slowly you can feel the soleus and gastroc muscles kick in. The first thing you feel is your soleus changing gears and going from eccentric to isometric. This feels like someone slapping the calf muscle just below the knee. When the gastroc kicks in next it feels like something poked you in the hollow behind your knee.

Next I will discuss how this works in skiing. Although some of you are probably getting the urge to rush off to the ski hill and try this you should control this urge. A whole array of things can prevent you from using the mechanism I have just described. And unless you correct them there is no way you will overcome these limitations.

Think about all this. You need to have a clear mental picture in order to understand how to apply it in skiing. More to come (of course). RicB we are getting to your question re an environment conducive to balance.

Next I will respond to the recent questions.
 
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#48
Quote:
Originally posted by David M:
First a few quick answers to nolo’s question after which I will start the jump to skiing since I know that is what everyone has been waiting for.

Nolo: David, would you go into this a bit more? It sounds like we can't line up forces on a shaped ski, and yet many experience "carving" on their shaped skis. What gives?
DM: Shape skis have been an important step in the right direction in many ways and a wrong step in many ways. It depends on the conditions and ski geometry as to whether you have a bad hair day or not. Your observations are relevant. The thing we need to consider is the type of snow. Hardpack and ice are solid-like. Powder is fluid-like. The mechanics are very different. Skis need to match the snow. More later.

Nolo: My understanding of the mechanics is that the reaction force of the snow combined with the anatomical events you have detailed deflects the COG inside the turn, which is a "centripetal force" that counteracts or balances the movement of the foot into supination or away from the inside edge ("centrifugal force"). 
DM: How would this provide the stable source of GRF your balance system needs??. More on this important issue down the road.

Back to using the walking model in skiing. Although equipment is a huge factor affecting performance let’s leave this until later and cut to what I see as the fundamental issue. The first thing that comes to the surface is that the physics of skiing are different than walking. I agree. 

Let’s start by assuming you are entering the 3rd phase of the turn in a strong ski posture (yes, this discussion is coming) and you want to initiate the next turn using the walking mechanics. The same forces don’t exist as in walking so you have to help create rhe required forces or at least increase the level force acting on you. Let’s use sailing as an analogy.

You are in the same position in the sailboat about to end one tack or jibe and start a new one. What forces are acting on the boat?

Gravity is pulling the boat down vertically – same thing in skiing.
Water buoyancy is pushing the boat up against gravity – snow pushes back against the forces applied to it by the skier.
Wind force is trying to push the boat downwind – gravity is trying to push the skier downhill.
The sailor is steering the boat into the wind – the skier is steering their skis into the hill against gravity and centrifugal force.

What is an knowledgeable sailor going to do to start the direction change so that forces come into play to turn the boat into a new tack?

Over to you nolo or anyone else who knows sailing and wants to tell us what should happen.
 
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#49
Quote:
Originally posted by John Dowling:
Actually, to tack you haul the mainsail in (tighten the boom). This causes the boat to roll to leeward (away from the direction of the wind). When the boat is pitched over, the lift of the sail creates a turning force that rounds the boat up into and through the wind. As you find your new course, you ease the sail again to its optimum angle to the apparent wind.

To jibe, you haul in the sail as you turn away from the wind, putting the trailing edge (rear) of the sail to the wind. Eventually, the wind switches sides of the sail and slams it across the boat, often dramatically. Hauling the sail in as you jibe (or gybe) helps you keep a little control of it. Unless you are windsurfing, in which case you can jibe by spinning the sail away from the wind (putting the leading edge of the sail to the wind) as you turn.

So I guess I don't understand how this applies to ski turns.

John
 
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#50
Quote:
Originally posted by David M:
Assume hardpack conditions. Your COG must be supported on your outside leg on a stable base of support (assume this exists – I will work out the details later). External force is trying to extend the knee of the outside leg and dorsiflex the ankle. This force is resisted by eccentric contraction. Your inside leg is flexed in isometric contraction with its foot higher than and slightly ahead of the outside foot. Although COG is supported on the outside leg the inside leg plays an intermittent role in helping to maintain balance. In this configuration your hips should be open to the fall line (counter rotated) so that the pelvis is passively adducted or turned into the outside leg and passively abducted or turned away from the inside leg. By passive I mean that the muscles in the pelvis that would actively abduct or adduct the leg are balanced through a parallelogram mechanism with the result that the net sum of opposing muscle tensions is zero.

The force of gravity is trying to pull COG vertically down towards the center of the earth. This force translates into a vertical force and a shear force acting down the slope. Because of acceleration COG has inertia. According Newton’s Laws COG will continue in motion in the same direction unless acted on by an outside force. Ignore forces like air resistance. The primary outside forces acting on COG are gravity and centrifugal force. They are both trying to pull COG down the fall line. While gravity just wants to pull COG down to the center of the earth. These are the natural forces in play. What is the only factor stopping these forces from changing the skier’s direction? The opposing force muscularly generated by the body applied through a stable base of support at the outside or downhill leg. 

While the outside leg has some amount of flexion at the knee the forces acting on skier are pulling against the flexor muscles with the effect that the leg wants to fully extend. The gastroc muscle, which is in eccentric contraction, resists extension of the knee. (No quads anywhere to be seen LM)

Pause and think about the inside (uphill) leg. What is it doing? The knee is much more flexed than the outside leg. But, it is more or less passively flexed by its position and the force of the snow pushing up against it. If the body were vertical to the ground and supported on the uphill leg COG would be much lower to the ground than if it were supported on the downhill leg. This affords the possibility of pushing against the ground by extending the uphill leg at the knee.

Where is the lead (uphill) leg in relation to the walk sequence? What does the skier have to do to get COG over top of and in front of the ankle of that leg?

John Dowling: “To jibe, you haul in the sail”
DM: You reduce the pushing action against the snow by beginning to relax the muscles of the outside leg. Do you fall over? No. Why not? Newton’s Laws. The force of gravity is acting on COG to pull it into the fall line. But it first has to overcome the inertia of COG. Result. COG starts to drop vertically and arc into the fall line. As it does it eventually has to cross over the base of support at the feet. (i.e. the skier has to jibe). At the same time the muscles of the outside leg are relaxing the uphill leg is actively extending at the knee in concentric contraction. As COG begins to cross over the base of support both legs are extended at the knee with concentric contraction. For a brief moment the skier is able to stand vertically on the slope of the hill. This seeming defiance of gravity is possible because of the inertia of COG and the force applied to the snow by the legs with active extension at the knee. It is important that flexion or bending at the hip be maintained in order to keep COG over the feet.

JD: as you turn away from the wind, putting the trailing edge (rear) of the sail to the wind. 
DM: As the skier extends at the knees the action of the extensor muscles rotates the legs into a neutral position with the pelvis (i.e. neither abducted or adducted) which is open or counter rotated into the fall line. This action turns the skier away from the forces. As the feet rotate under the pelvis the old outside leg comes under COG and the new inside (old outside leg) becomes the new lead foot in the walk sequence. The effect is due to extension having created the up and over levering action required to move COG in front of the ankle joint. 

JD: Eventually, the wind switches sides of the sail and slams it across the boat, often dramatically.
DM: To complete the process the skier continues to rotate the legs simultaneously to bring them across the fall line. This establishes the same position COG in relation to the base of support at the new outside that it had with the old outside leg. The walk sequence is complete. Creating the abducted, adducted relationship of the legs with the pelvis by actively rotating the legs produces the same result as the passive process associated with walking.

One last thing. Having established the foot position under COG the skier must relax and settle onto the outside foot. Why? To allow the forces to turn on the stretch reflex by stretching the muscles in the back of the legs and the back (as we will see when we get to stance). You have just jibed on skis. 

This is the physics of how the forces are used. However, a whole array of obstacles stand ready to prevent you from actually performing this feet. Simple things like too much forward lean in your boots for example very common) will make it impossible to make the moves described as well as preventing you from using eccentric contraction in any kind of useable way. 

Any questions?
 
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#51
Quote:
Originally posted by David M:
LM: "We as skiers are capable of moving in multiple planes, so by equalizing the forces in any given plane, we can use this to our advantage. We can remain semi- relaxed, able to create our next move. For if we are not relaxed, and the muscles are already active, they can not do anything else until they do become relaxed.
This is a very common issue with recreational skiers- they do not understand that muscles can only do one thing at a time, then must be relaxed prior to their next operation. Instead, they try to go from one movement to another without relaxing, resulting in involving larger muscle groups to overcome the resistance of the original muscle."

DM: Lisa Marie is it ever great to be in such good company! A few other issues to consider:

1. It is not practical (not to mention possible) to consciously orchestrate muscle activity to create balance. Yet many articles on ski instruction suggest processes that would pretend to do exactly this. Utter nonsense. The writers of such gibberish should spend some serious time in medical libraries.

2. If a muscle is in eccentric contraction other muscle in the same family can not be in concentric action at the same time; i.e. muscles can not be lengthening and shortening at the same time!

3. If you are fighting the forces you are most certainly using concentric contraction to ski. Unfortunately, widely read ski magazine articles are suggesting that the ideal skier should be a WWF wrestler.

LM: Muscle synergy. Don't go skiing without it!!!
DM: I second that. FYI I helped launch a human performance company called synergy. I chose the name for a very good reason.
 
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#52
Quote:
Originally posted by David M:
LM: Sarah Schlepper. The first time I watched her race, was on OLN, a WC event which also featured Janica kostelic. What a contrast. Kostelic looks like she is barely working, but her race results prove otherwise.
DM: Very astute observation LM! I am truly impressed. If you watch video of a Kostelic in slow speed you will see her make exactly the walking movements with the associated eccentric muscle action I have just described. 

I concur with your comparison. Assuming Schlepper and Kostelic were athletic equals how much of an advantage do you think Kostelic's movements give her. 100, 200 or 300%. How about more? 

...
 
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#53
Quote:
Originally posted by John Dowling:
Nolo- In windsurfing, at least at higher skill levels, no one ever tacks. The small boards do not have enogh momentum to move through the wind. When you jibe, it's easier to spin the sail so that the mast (instead of the trailing edge of the sail) face the wind. That way the the wind changes sides of the sail calmly as in a tack, even though the boat is actually jibing. 

DavidM-I guess I don't like this metaphor because my view of sailing is that you deliberately power up before turning, sometimes to the point of putting the boat nearly out of control (as in power tacking a race boat) while in skiing the power comes as you release the turn you are finishing. I understand all those descriptions of ski turns, but it doesn't relate to sailing to me. 

John
 
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#54
Quote:
Originally posted by David M:
John DowlingavidM-I guess I don't like this metaphor because my view of sailing is that you deliberately power up before turning, sometimes to the point of putting the boat nearly out of control (as in power tacking a race boat) while in skiing the power comes as you release the turn you are finishing. I understand all those descriptions of ski turns, but it doesn't relate to sailing to me. 

DM: John I don't think you understood all the descriptions. 

This is not a passive process where you trickle into the fall line. You do deliberately "power up" to the point of losing control.

You start the movement into the fall line by relaxing the outside leg. But the forces required to power up your uphill leg so it is transformed into a stable base of support (it isn't at the this stage) are not sufficient in this environment. So you have to create the necessary forces by extending first on the uphill leg and then extending on both legs. When you do this you launch baby. And you don't just launch into the fall line either. You launch UP and into the fall line. And when you do you had better be supremely confident of the forces because you are sending your precious body to the place skiers fear the most. 

If this isn't powering up to the point of losing control (serious injury or death comes to mind) then maybe we are speaking different languages.
 
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#55
[What determines individual forward lean requirements? First and foremost is the critical angle at which your ankle joint switches to isometric contraction. This angle should be shaft angle or lean of the boot where your calf rests against the rear cuff. You need some free space to flex forward from here. We will get into this later.]

I can ski with my boots unbuckled (very soft flex), but I have never found free space to the front (or back) a useful feature. I want "progression" and free space gives a bang (dual rate) when I get to the boot. That is why I choose to snug the "Power Strap" up against the boot liner and not the boot shell. 'More progression.

I was pleasantly rewarded while skiing Saturday with the responsiveness and solid traking (tip to tail) when I pressured the tips of my skis. "Dust on Crust" conditions. These old school methods really do work!

CalG
 
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#56
Quote:
Originally posted by Ric B:
...
I've had my students describe this as climbing the stairs. you can give them this feeling of release and the natural tipping that follows on carpet if you want. Simply stand relaxed knees slightly bent, feet a narrow hip width apart, then have them just slightly pull one hip upward, straight up. The result is the transfer of COG to the other foot over the little toe side and a resulting rolling of the foot and movement of COG away from the contact point. Do this on snow, and direct the awareness down to the feet and light bulbs go off. 

What you are doing by releasing with a relaxation and an inside extention is a constant movemnent to be long from the inside shouder to the outside foot through the middle of the turn. a strong skeletal stance. The hip is critical here. How can we direct our energy to the outside foot if our outside hip is higher. That's a contact point thats not equal to the challenge. for me, more important than rotation of the hip, is the hip being tilted down to the outside. This is one of the good angles everyone talks about in good skiers. It's a sublte amount of tilt most of he time, and it's there in all good skiers, and yes it is a very similar to the movement of the hip in walking. We can't find that "equilibrium of the forces" if one part of our skeleton is acting out of sequence. Out of the mouth of my Tai-Chi instructor last night "movement is started at the feet from your root, powered by the legs, directed by the hips, and felt in the body. 

How do we find new ways to introduce this structural awareness and sensitvity to begginers and low level skiers? How do we help them recognize their natural balance and skeletal movements in the context of skiing and the equipment they're using? DM, I would still like to know what you did in your experimnets to find the "enviroment that is conducive to balancing". [img]tongue.gif[/img]
 
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#57
Quote:
Originally posted by nolo:


Once a student experiences the sensation of standing up down the hill there's no keeping them in a traverse. Now they start experiencing the turn from FALL-line to Fall-line.

Love that hang time! It's the intermittent reinforcement that makes turning so much fun.
Also, I don't know if walking is as tangible an analogy as pedaling would be. The hardest sell with students is their perception that dealing with stronger forces must mean exerting more force. It is counter-intuitive to think that trying hard might be counter-productive. .
 
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#58
Quote:
Originally posted by TomB:
DM said: You start the movement into the fall line by relaxing the outside leg. But the forces required to power up your uphill leg so it is transformed into a stable base of support (it isn't at the this stage) are not sufficient in this environment. So you have to create the necessary forces by extending first on the uphill leg and then extending on both legs. When you do this you launch baby. And you don't just launch into the fall line either. You launch UP and into the fall line.

Are you sure you want to emphasize the extension of the uphill/inside leg (soon to become the new outside leg) to that extent? Why all that effort to step up to the inside leg? Why not just let the body fall to the inside of the new turn by releasing the old outside leg. There are plenty of forces on you to pull you that way anyway. Are you trying put the skier back in that eccentric contraction? Do you really need to straighten that new outside leg to achieve that? :
 
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#59
Quote:
Originally posted by John Dowling:
</font><blockquote>quote:</font><hr />Originally posted by nolo:
The hardest sell with students is their perception that dealing with stronger forces must mean exerting more force. It is counter-intuitive to think that trying hard might be counter-productive.
I sometimes explain that concept in this way: If you were a racer, the forces generated by your turns would increase with increasing speed. Therefore, the maximum speed you could travel through a turn must be limited by your ability to resist those forces (strength). If you are using all your strength to resist the centrifugal force of the turn, what can you do to contol yourself? The only thing that does not require more strength is to relax the outer leg, and allow momentum and gravity to take you out of the turn into the new one. 
DM- I understand rebound and powering out of turns, but to me it's just not the same as powering into a turn in a sailboat.

John
</font>[/quote]
 
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#60
Quote:
Originally posted by Ric B:
...
I don't want to talk for DM, but I think the point is that relaxing the outside leg imediatly tranfers the COG and pressure to the new outside foot. It's the slow and deliberate extention of that leg that fully engages the edge. If there is no extention, if the leg muscle is doing isometric work, then you have to wait for the edge to fully engage because the body is already tipping into the turn. It's not a step up, as the COG is imediately moving away from the new point of contact, and the extention is helping the COG move in that direction, or simply put, the extention is to the side, because of the all forces at work. If you looked at the foot movements by themselves, suspended in the air, you would see the feet pumping up and down. The extention allows the long skelletal posture in the middle of the turn. Long and short, empty and full. How can you have an edge without first establishing contact? and how can you establish effective contact when gravity and centrifigal force are moving your COG away from that contact point. You have to grow your root and initiate from the new contact point, and you need to extnend that new leg from your contact point to achieve this. This is (and I'm on shaky ground here), the centripetal force that makes a turn. Have at it folks! [img]tongue.gif[/img]
post #4 of 28
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Quote:
Originally posted by David M:
RicB
You are definitely very much in the right direction here in terms of relaxing the outside leg to get COG moving in the right direction (i.e down the fall line) and transfering COG to the uphill leg. Although the physics are a bit more complex the concept is basically right. I need to get into more detail on the reasons why you need vertical force to load the foot. It has to do with correct activation of the foot's sheet-like ligament, solidfying and reinforcing pronation and moving COP (not COG) to the ball of the big toe.
 
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#62
Quote:
Originally posted by David M:
Issues relating to a Conducive Environment

“The human lower limbs are one of the most sophisticated systems ever to have arisen from evolution”.
(Can’t recall the source. I have a lot of reference books.)

“Gait (walking and running) is the most common of human movements. Although we usually take it for granted it is one of the most complex and totally integrated movements. It has been described and analyzed more than any other total movement, and scores of laboratories are dedicated to the assessment of gait both normal and pathological”
The Biomechanics of Motor Control of Human Gait: Normal, Elderly and Pathological (2nd edition, 1991) – David A. Winter (past president of the Canadian Medical and Biological Engineering Society).

Winter on recalling our experience as a child before we could walk:
“We see others walking, see what they can do with their walking, what we can not do, and we want to do it too. So, lying on our back or face is not enough. We struggle to crawl – then we crawl everywhere we can”.

Remember this? How soon we forget how long and hard we struggled just to get upright.

I disagree with Winter on one point: skiing is one of the most complex and integrated total movements. It is far more complicated than walking. And as we have learned through experience we do not need a ‘Body Owner’s Manual’ to walk. However, we do need such a manual to ski as easily as we eventually learned to walk. In skiing as in walking we have to crawl first.

Why the strong extension?
There’s a reflex in the body called the ‘inhibitory reflex’. It’s job is to prevent you from doing certain things until it has confirmed that the system responsible for performing the action is ready and especially, to ensure the resulting action is safe. In golf it takes 30 horsepower (yes 30 HP, not 3!) to accelerate a driver from zero to 100 mph! The available horsepower in the arms doesn’t even come close to meeting this. Where do you find such power? In the trunk, especially in the abdominals. The speed at which the spine can rotate is directly related to club speed at ball contact. More is obviously better. If the spine is not adequately stabilized by muscles the inhibitory reflex will limit the speed that the golfer can rotate the spine.

“Screw this” you say. “I will just try to rotate faster and override the dam reflex”. This doesn’t work because the body is smarter than you are. If you try to do stupid things in some situations the body will intervene and stop you. Trying harder will only result in you flailing with the arms. The only way to change this is to give the body what it needs. You have to increase the stability of your spine before it will let you rotate it faster.

A similar situation exists with regards to your feet.

In order to come up to power-up to a stable base of support the aches of the feet need to acquire both tension and stability against an opposing ground reaction force (GRF). The normal tensioning sequence starts in the adaptive state. The lead leg switches from the unloaded state to the adaptive state when the outer aspect of the heel contacts the ground. This is followed by contact of the outer or lateral aspect of the foot and, lastly, contact with the transverse aspect of the foot (i.e. across the balls of the foot from the small toe to the big toe). 

At the initial contact of the heel COG pushes the foot forward into contact of the outer aspect of the foot with the ground. As COG comes over the top of the ankle (big ‘IF’ in skiing as in “if it can”) COG squashes (compresses) the arch vertically against the ground force. This tensions the arch triad and drives COP to the ball of the big toe (as far inside as it can get) in preparation for what? In preparation for the old support leg left behind to swing past the new support foot. When it does the body has to be able to push away from the swing foot in order to not fall towards it as it comes by (Newton again – “for every action….”. 

What muscles does the body use? Since the foot is pronating, the sole of the foot is turning away from the center of the body in eversion. Eversion is opposed by inverter muscles acting in…… ? You got it. Eccentric contraction. In the above process COP does not run down the center of the foot. Instead it runs along the outer aspect then arcs across the forefoot to the ball of the big toe. This latter effect which is critical to a stable base of support on which to resist the external forces is traditionally thought of as ‘edge control’.

What else should be happening as the arches of the foot are being tensioned?
The heel bone is angling inward on a vertical axis, rotating inward about its contact point with the ground on a horizontal axis and dropping on its toe end. This process is accompanied by the ankle side of the metatarsals rotating on a horizontal axis towards the inner aspect of the foot. Concurrently, on the toe end the metatarsals are spreading like a fan opening. The foot is also getting longer and the top of the arch is dropping. One last thing. The foot is pronating. So the tibia is rotating (with the knee) into the center of the body (medial or internal rotation).

While all this is taking place the foot is still in the adaptive state. The supportive state is on standby awaiting confirmation by the inhibitory reflex that “the Eagle has landed”; i.e. that the foot is capable of supporting the body. How does it know when the foot is ready? The foot is ready to support the body when all 3 arches of the foot have found solid opposing resistance from the ground and the reflex is confident the application of force by COG will not destabilize the foot. Here we make one huge erroneous assumption; our ski boots, bindings and skis are the ground. Not according to Newton. Equipment is a quasi-ground. We still have to get to the snow to connect to the ground.

Getting to the ground drives the requirement for a ‘conducive environment’ that let’s your foot function. Here the present situation would be laughable, even hysterical if it were not so patently absurd. While experts wax poetically on the importance of balance out of one side of their mouth they simultaneously preach confinement and even complete immobilization of the entire foot and leg in the name of improved balance out of the other side. This a bad joke right? Not at all. These guys are dead serious. One has to wonder what planet they have come from.

About a conducive environment. It is an environment where all the described actions must be able to occur without interference that would significantly impede them. What kind of things? Adequate width in the shell for the forefoot for starters. And adequate room for the midfoot to move inward and the heel bone to roll inward on its axis. If the inhibitory reflex detects that even one of the myriad of required actions is impeded it puts the supportive state on hold. As far it is concerned the foot is still adapting to the terrain. It is still seeking contact with the ground. It will not be ready support COG until it has satisfied the inhibitory. The message you get is “sorry, you have to try again.” 

“ Screw this” you say. I am going for it anyway. Your prerogative. Flail away baby! [img]tongue.gif[/img] 

TBC
 
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#63
Quote:
Originally posted by Ric B:
Up is a relative thing. For me when you add the other forces involved in sking and their effect on the body, and we allow our body to read them like simple gravity on a flat plane, up from the contact point becomes away from the contact point, relative to "all" the forces working together. Really slow speed turns will show more "Up" of the COG, but for really high speed dynamic turns, up is a different direction from whats needed to move the COG in the direction of the new turn and away from the contact point. 

Your foot and lower leg mechanics make sense to me, but there may be more than one way to have them integrate into our skiing. We can say being barefoot is the best way to be rooted into our contact point, but how many of us go through the day barefoot? Depending on the task at hand we choose our footwear. If we are doing something that will put excess force on our foot we opt for more support. I worked construction all my life. I never wore the same footwear doing trim as I did if I was stacking a log house. The loads placed on my foot moving and lifting the logs would quickly wear out my foot if my choice of footwear didn't offer enough support to my foot. This light weight boot allowed plenty of foot and ankle movement but had a limit to these movements that allowed some support. How my foot feels at the end of the day is directly related to how effective I was at choosing my footwear. So ski boots are they perfect? No. Footbeds are they perfect? No. They are a compromise to achieve a desired result. We can't just stand on our skis. We need a physical connection between our skis and our foot. So what did you do to create an enviroment that was conducive to balance, and I will now add, that still allowed an effective connection to our skis? What changes to the equipment were made? 

I ski a softer boot than I used too. It has a progesive flex, meaning it starts soft, and smoothly and prgressively gets harder. This allows much greater range of motion in the ankle. But they are still stiff lateraly. This allows a solid connection to my ski edge. My footbeds intimately support my foot to reduce the stress placed on it by the forces of skiing (my old footbeds always find a home in other shoes and boots). They reduce the movement of my foot in a way that reduces the stress that causes my foot to feel wornout at the end of the day. What science did your experiments find that conclude that our ski boots and footbeds are illconieved? And what changes did your science prove are nessasary to achieve an enviroment conducive to balance? 

Yes, what about powder? My take is that when the surface becomes soft we root by directing our energy down our structure and through our foot. The difference as I see it is that our POC of the ski stays in the middle of the ski as opposed to at the edge of the ski. As has been said before, we ski on the bottom as opposed the edge. How this affects the mechanics of the foot is a good question?

DM, I don't know that I'm seeing the same path as you. Help me see it. [img]smile.gif[/img]
 
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#64
Quote:
Originally posted by CalG:
Regarding the inhibitory reflex and the requirement for the foot to sense support in three aspects before one can commit to "standing on it". 
I have felt this inhibitory reflex many times, and it seems to be "modifiable" by association. That is, if I think, or know there is something around me I do not wish to step in/on, As I contact the slightest irregularity on the floor surface, this reflex will pull the plug on adding additional weight to that foot. Sometimes by subtle rolling of the foot to redirect the transfer of weight, but usually by collapsing the big muscles in the upper leg.

This happens many times playing adult soccer. If I feel that my foot may be stepping on another's, my leg goes weak beneath me in order to prevent an undesirable result by full weight transfer. There is a perfectly good surface there to stand on (someone elses foot  but "I" have choosen to reject this option and have so instructed this inhibitory reflex. 
And it works faster than I could ever do on my own.

Applied to skiing, I can see the value of foot beds that really fit the foot. A truely comfortable boot fit. The sensation of even support will always be available, only to vary in pressure magnitude. We train this inhibitory reflex to accept the force sensations present as sufficient in anticipation of the real forces that will develop. When traveling over an uneven surface, the support muscles must be in an alerted state ready to accomodate large changes in position and still provide "correct" pressures. The body mass in motion representing a load that may be 1,+/- 1 G at any time.

CalG
 
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#65
Quote:
Originally posted by David M:
nolo: OK remember that I said the hard pack is solid like and powder is fluid like. In powder the weight of your body pushes the snow away from you whereas in hard pack you have to cut a platform to stand on. In powder you ski on 2 skis because you need a large flotation base under you. You still develop a platform because you sink into the snow until you compress it under you into a base dense enough to push back. Newton's Laws again.

As to the issue of numbing the inhibitory reflex you are right. This can be done. After a great deal of persistence you can also reprogram the body do function in incredibly stupid and inefficient ways. In a very real sense your are causing it to revert back in the direction of crawling.

Reference is made by RicB to flexing the boot with the ankle. Can anyone tell the group what muscules you use to flex the boot?
 
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#66
Quote:
Originally posted by David M:
Powder skiing. You guys are good! 
nolo: Yes, I think the free fall required to compress the snow freaks out the balance system.

Like balance everyone keeps saying you need to be strong to flex a stiff boot. Am I to believe no one else has any idea what muscles are involved. How can you increase the strength of the right muscles if you don't know the answer to this question??

Flexing the boot

Try this. 

1. Put your ski boot on (one boot will do) and deep flex it. 

2. Sit on a table with the same leg suspended and flex the boot exactly the way you did on the ground.

3. Think about the results.

4. Tell the group which muscle flexed the boot and how it works.

1st Breakthrough revelation: Skiing does not require all movements of the foot.

Pronation involves rotation of the long axis of the foot and the vertical axis of the ski into the hill.

Supination involves rotation of the same aspects away from the hill. 

Which one is essential to skiing?
[ November 25, 2002, 12:49 AM: Message edited by: disski ]
 
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#67
Quote:
Originally posted by Notorious Spag:
TomB. I didn't feel like wading through 9 pages of this right now. I will later so that I can get more out of this. But I have a question for you (and feel free to retort, anyone, I'm just exploring a little).

You stated that the cross under situation in powder is similar to the same situation on hard pack. That there should be no difference. My stand would be that although the movement might be similar or even identical, but the application is totally different. Tom, would you think that our POSITION, with relation to the hill, in both instances is identical? I only want to talk about this because I'm Curious George right now. 

On hard-pack, we tend to build up "gravity" forces throughout the turn. The best way to monitor these and control speed is to make a round turn, where we finish with our skis facing across the hill. Now when we cross under, our center is projected Down hill, or toward the path of our next turn, whichever applies.

In powder, our skis will tend to "float" a little and "look" for a plane of existence that is more level than the pitch we are skiing on. The platform you were discussing isn't at the same degree of pitch as the mountainside. 

Also, the platform we build when skiing powder can only give back to us what is put into it. Try straight-lining through the pow and let the skis find level... now bounce once. Your "platform" has just disintigrated and changed for an instant. It's not a constant. Groomed hard-pack, on the other hand, is much more reliable. A skier can put everything they've got into the snow and it will simply give it all back, with more where that came from. It's surface can be counted on and trusted, and the skis will glide across the same pitch as the mountainside. 

So our tactic in powder, as opposed to hardpack, changes from speed control via edging and turn shape to speed control via pressure control and turn shape. When cross-under happens, we can move more intuitively... not so much downhill, while simultaneous with a deliberate rotation of the legs. Because I'm standing more upright, and not relying so much on edging movements, it's really closer to doing low-level, skidded parallel turns than it is to carving on groomers. I realize you never mentioned carving, but there is a difference between high end Pow skiing and high-end Cord trenching. 

All the elements are still there, but the blend and intent of those elements are only barely related. 

2 cents,
Spag :
 
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#68
I do the power strap on liner bit too - under direction from instructor....
 
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#69
Quote:
Originally posted by David M:
While nolo and LisaMarie solve the dorsiflexion problem I will get back to the issue RicB raised about 3 light years ago – the illusive CONDUCIVE ENVIRONMENT.

“The human foot is one of the most dynamic organs in the human system”. 
Translation: The elements of the foot move with each other in 3 dimensional space against fixed references. And, by the way, they move significantly and continuously.

If we render the elements of the foot…..what is that word that boot fitters love to use? Ah yes, Stable then what? 
TRANSLATION: Make it undynamic – no movement – lock the sucker up. 
Is this a good thing? Probably not. It can not only greatly increase the effort required to ski it can decrease the effectiveness of the lower limb’s defense mechanism against injury from the interaction with the snow by up to 1000%. Does anyone want to put this in his or her marketing pitch? Probably not.

So the boot has to allow the elements of the foot to move between the space they are working at in two footed weight bearing (bipedal) and the space they are working at in one footed weight bearing (monopedal) under the maximal skiing loads. This means the lower boot shell or tub that your foot sits inside must have:
- Sufficient width for the maximal spread of your forefoot;
- Sufficient width for the maximal inward movement of your ankle bone and the structure of the midfoot, 
- Sufficient clearance for the soft tissue running along the inside of the foot between the ball of the foot and the midfoot, and
- Sufficient clearance for the movements for flexion of the ankle bone.

Why? So the foot can be fully loaded (compressed) in order to power-up its truss-like arch structure. If this doesn’t happen the skier does not have a strong foundation on which to construct a structural column on which to support COG and initiate eccentric contraction from. Pretty compelling reasons. We are only talking about the lower shell your foot sits in here. How about soft or stiff? If it has the right clearances you can make the shell out of steel if you want. Stiffness is not the issue. Clearance for the dynamic requirements of the foot is. 

SIDEBAR: What about the new ‘soft boots'. I have been there before the current crop hit the market. The challenge is to make the structure stable enough. Once you open the throat this is almost impossible. Would I ski in them? Are you kidding!

Since I will begin to talk about manufacturing considerations soon it is timely to advise you that I have been involved in every aspect of ski boot manufacturing from design to molding and assembly and field modification. In addition, I assembled boots from raw factory parts for some of Canada’s most successful racers including our Crazy Canucks. The reason I am telling you this is that I will be revealing the reasons for certain decisions in boot design and construction and how they affect you. In this arena I know precisely what I am talking about.

There are potentially very significant issues with anything your foot sits on the shell. These include the boot base or boot board and any kind of footbeds or orthotics. So far as I know I am the only party to have been involved in testing footbeds during actual skiing. At least 50% of those tested caused serious problems; they made you ski worse. While there are lots of opinions and theories as to why they are good, until their effect on the skier using them is proven with foot pressure data synced to video they are just that; opinions and unproven theories.

More later. I am off for the next 3 days so hope to get deeply into this issue.
 
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#70
Quote:
Originally posted by David M:
Nolo: ".....we want to talk about the peroneals since they are the principal everters".
DM: Careful here nolo. If we want to use eccentric contraction do we want to shorten a muscle to create a movement? 

Principle: Muscles in the same family (i.e. extensors) can not be in eccentric and concentric contraction concurrently. 

In other words separate related muscles can not have one lengthening while another is shortening. Keep going. Think more about this.

Re conducive environment
One very important thing to add to the lower shell requirements:
- There must be room for the toes especially for the big toe to sit in its correct alignment which is straight ahead. 

The reason the toe box of the shell is a half circle has to do with the DIN binding standard. It has absolutely nothing whatsoever to do with the functional requirements of your foot. NOTHING!
 
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#71
Quote:
Originally posted by nolo:
What David is saying rings a bell. When I was in the men's boots I definitely was in dorsiflexion at turn's end: 1) stiff race boot, sized down; 2) high boot, large calves; 3) the aggro forward lean was adjustable, the rear spoiler removable, but the boot shaft was strangling my calves, causing my feet to fall asleep on the chair, and I needed to install boot heaters to keep my formerly severely frostbitten toes alive. In the junior Dolomite Sintesi, I have not felt the need to heat the boots ever, with only dance tights on my feet. This alone improved my performance. How can you ski with numb feet? 

I was a woman in mortal combat with her boots. No wonder women drop out at a higher rate than men. How do I know that? The statistics tell me so.
Nolo:

Do these Dolomites have a *very* narrow heel by any chance?

My wife experiences many of the problems you describe and has painfully endured ski boots for years. She's currently in the Lange X8 (or something like that - I'm terrible in that I can't really say what she's got) with custom liners, etc. 

I want her to try new boots, but most everything she tries has so much space around her heels that they end up doing all kinds of modifications. It's best if she can start with a boot that has a fairly narrow shell in the heel. 

Any thoughts?

Thanks,

Bob
Bob Peters Jackson Hole, WY        
North40 Realty
     
Me on twitter - http://twitter.com/bobpetersjh
 
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#72
Bob,

They fit my heel, which is fairly narrow, and have a wide toebox. I found them a perfect fit for my pie-shaped foot. I had to dremel out a bit more space forward for my toes. There's plenty of plastic up front for that.

Plus they are the most beautiful color! I think sno'more would call it pomegranate. 
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#73
Quote:
Originally posted by nolo:
Bob,

They fit my heel, which is fairly narrow, and have a wide toebox. I found them a perfect fit for my pie-shaped foot. I had to dremel out a bit more space forward for my toes. There's plenty of plastic up front for that.

Plus they are the most beautiful color! I think sno'more would call it pomegranate. 
So I went to the Dolomite site...

http://www.dolomiteusa.com/ski/dolomite-sintesi85.html

and looked up the Sintesi. There are four Sintesi models listed and three junior models listed, but no (that I can decipher, anyway) Sintesi Junior.

Can you tell from this site which boot is yours?

Thanks,

Bob

Also, for a hopelessly color-challenged male, what color is pomegranate? Is it red?
Bob Peters Jackson Hole, WY        
North40 Realty
     
Me on twitter - http://twitter.com/bobpetersjh
 
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#74
Bob,

I am in the Sintesi 7.5T (T=Team), which is not listed on the site, but I believe they still make this boot. It's not pictured in my rep's brochure, but it appears on their model chart, so I assume it's still in production. Check with your dealer on this.

The Sintesi 7.5 or possibly the 8.5 are worth checking out. The fifth buckle, as they claim, will keep any skier's heel in place.

Pomegranate is red, like the fruit.

Let me know what you find out, please.
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#75
Zowie. Are we on a roll or what! [img]graemlins/thumbsup.gif[/img] 

It is amazing how the pieces are starting to fall into place. This post is just to let everyone know that I will keep going. Heck I am just getting up to speed. Thanks all for your terrific input. Awesome dsski. Yes I know Roger Systad - heck of a cook!

I hope that everyone is starting to get the message that a good postural assessment is the place where everything should begin. Over to you Lisamarie. 

The next thing in line is a stance or ski posture that maximises the stretch reflex all the way from the heels to the shoulder girdle. I am getting to this as it is crucial (heck everything is crucial). Please don't start to think that a good posture is bolt upright because I say your boots have too much forward lean. This is not the case.

RicB, yes I will tell you how you determine the critical angle of your ankle joint. On a related matter what you said about rising up on the balls of the feet when your boots have too much forward lean is right on. You made the jump here. What typically happens is that skiers try to get more upright by pressing back against the spoiler of the boot. In many cases I observed with pads that recorded sole pressure during skiing skiers are hanging forward on the balls of the feet with the heel completely off the base. This may feel a lot better but it is a receipt for disaster because you are not connected with the ground. To your brain you have not touched down yet. So any forces that disturb you will try to complete this adaptive process. The result is instability.

I will respond to your other questions later. Unfortunately I am tied up this week doing some things for my wife's business and she gets priority. So I will be sporadic. But I will try as best I can to keep up. This thread is fast developing a life of its own.

Insofar as my research we offered it to the ski boot industry back in 1992. They said;

1. We are not interested in even seeing it.
2. We might be a bit interested later but not now.
3. We are somewhat interested.
4. We are hugely interested.
5. We want to spend the rest of our days with you.
6. We just want to go skiing.

Hint: There may be more than one answer. What do you epic ski members think the industry said?
 
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#76
#1.
Become an EpicSki Supporter and get access to special deals, special site privileges, and the private forums. 
 
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#77
nolo wins. The correct answer is #1.
 
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#78
"I hope that everyone is starting to get the message that a good postural assessment is the place where everything should begin. Over to you Lisamarie."

David, based on my discussion of postural distortion in my thread, do you think that some people end up in boots that actually reinforce these distortions?

also, re your research, I once wrote an article for submission to the PSIA journal about balance exercise for ski conditioning. they never even acknowledged it! :
 
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LM not only does ski equipment reinforce postural deficits boot fitters get into the picture and start cramming footbeds, wedges and other gimmicks under the foot in an attempt to improve human aesthetics. This usually makes things much worse. Physios and chiropracters regulary treat knee, hip or back pain or a combination of them here in Whistler and then find out it started after the client had their boots custom fit. 

"The problem my dear Brutus is not in our stars in ourselves in that we are underlings. We know not what we do." Shakespeare

I think the above quote is appropo. Hopefully I have not savaged Shakespeare.
 
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Disski: DM, a question, where in the process of transferring the stability of your balance structure to the shin and heel does support for the rear of the knee become critically compromised by the soleus needing to become less active in the balance process? 
Is this a progressive, or an on/off type of loss of support.
DM: It can be either. It depends on how rapid the ankle rotates. 
There a 3 possible scenarios:
1. The forward lean angle of the boot is correct but the skier consciously reduces contraction of the soleus so s to press the shin into the boot tongue.
2. The forward lean is too great. This forces the skier to use the back of the cuff for support (i.e. they are in the back seat).
3. The skier has the same forward lean as in 2. but they deep flex the boot by squatting and hanging forward.

In the first scenario the soleus will passively lengthen by the progressive relaxation of the muscle. This is a scenario that never happens when the balance system is in control because it orders the soleus to contract against a lengthening not reduce contraction. Here the soleus has been consciously over-ridden initially. Over time repeated movements will re-program the balance response to reduce contraction automatically in order to allow the soleus to lengthen. The result is no eccentric contraction and a huge and progressive decrease in both power and sensory input required for balance.

In the second scenario there is no contraction of the soleus because the ankle is rotating in plantarflexion. Here, the leg below the knee and the foot are in the unloaded state. In effect they are dead in terms of providing active support and balance.

Scenario 3 puts the skier at risk of a complete and rapid release of the soleus because the large joint angles at the knee and hip require a rapid increase in dorsiflexion to prevent a forward fall should the skier suddenly load the boot by entering terrain that applies a strong upward force to the shovel of the skis. This could be a mogul or a ridge in the snow surface.

Dsski: Is the entire knee compromised or just specific directions. 
DM: It depends on the nature of the force and the manner in which it enters the lower limbs. The big problem is the soleus is a major absorber or energy in eccentric contraction. So the loss of EC is serious at any time. Research done at UC Berkeley’s Dept of Mechanical Engineering has shown that a skier is on the threshold of injury during normal ski maneuvers. A paper by the head of the dept. called ‘The forces of skiing and their implication to injury’ concluded that muscle intervention is one of the most important forms of protection yet the least studied. One has to ask why. The 2 structures most at risk are the tibia and knee.

Is the point where the soleus turns on and off during walking and flexion the same point as when it is placed in a 'correctly' fitting boot or does the boot change the point.
DM: The angle of the ankle in dorsiflexion where the soleus switches to EC (eccentric contraction in future) is the same. In the walk sequence the soleus stays in isometric contraction (IC) until toe off of the support foot. Here, it locks the angle of dorsiflexion of the ankle until toe off. 

In upright postures the soleus is pulsing off and on in eccentric contraction to maintain balance. In this process the net angle of dorsiflexion changes very little. The action is similar in skiing except that we need a posture or stance on our skis that exaggerates eccentric contraction and. Here the angle of dorsiflexion should not change much because the position of COG cannot be effectively controlled by the balance system if the angles of the ankle and knee become too great.

Dsski: Thanks for your knowledge and time.
DM: You are welcome. Hope this helps.

Milesb:
David, I have a couple of questions.

1. What are the drawbacks (performance and safety) to using boots designed to your criteria?

2. Have you done similar research on snowboarding

First off, according sound principle this boot should be much safer than conventional boots for 2 reasons:
1. It introduces much less static (confusing data) into the central nervous system. This equals better response action and timing.
2. It potentates solid compression of he ankle and knee joints (This increases stability by up to 400%). In addition provides an environment conducive to the maximum power in eccentric contraction which is 200%-800% that of concentric contraction. Why am I so confident of this? Because the National Research Council of Canada nominated my invention for the gold medal in both science and engineering in a prestigious competition. In order for the nomination to go forward 3 scientists recognized in the related field had to support it. In other words they had to put their credentials behind it. They did. One scientist called my invention “an enormous step forward from conventional thinking”. He also stated it was safer than a conventional ski boot. I think this says volumes about conventional boots.

More later. It is getting late. Thank you all for your interest and questions.
[img]smile.gif[/img]
 
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I didn't write any of that stuff in the post above - David you need to learn to use the quoting.....

Roger is one of my instructors(the newest regular one) [img]smile.gif[/img]
 
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disski oops you are right. [img]redface.gif[/img] 

It was joel quoting you that got me started. I normally copy a thread to Word and then disconnect. I would rather think off line.

Any I hope I answered joels questions.
 
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I'm posting this here because the other thread is likely to be dead. Most of this pertains to things brought up in the other thread: "Balance" I'm trying to distill the thread down to the nitty gritty in order to learn it. If this is confusing let me know I'll delete it.

"Balance"

Questions are next to the *.

(The easiest way to view the whole thing is to click on "printer friendly view" on the bottom left of any page. This creates one huge document (104ppg). Then if you use "print preview" from the file menu you can quickly skip from page to page in that window or scroll the document in the other window.

I'm trying to sum up the most basic concepts for your entire approach. They seem to be eccentric contraction, the 'stretch reflex' (still don't get this one), the transition of the foot from the adaptive state to a stable state, and the 'inhibitory reflex'.

(All quotes are from David M unless noted) 

The muscles:
Quote:
An example of concentric contraction is the flexing component of a bicept curl. Here the weight is being accelerated. The extension or return movement component uses eccentric contraction. Here the weight is being decelerated against what force? Gravity.

A muscle in concentric contraction does not change (and can not change) to eccentric contraction if it is overpowered by the resistive load. Instead, it shuts off completely.

Muscles in eccentric contraction can develop 2-8 (200-800%)times as much power as muscle in concentric contraction. The power curve increases with the load until it is finally overpowered.

The power curve of muscle in eccentric contraction increases exponentially with the rate at which muscle is lengthening once a threshold level has been exceeded. - 11/16, 6:29pm; pg38
Quote:
One reason the advantages may not be apparent is that muscles in eccentric contraction can use the stretch reflex

... COG lies in front of the ankle. This creates the tendency for gravity to cause us to fall forward. Muscles in the back of our leg are stretched by gravity. They contract to oppose the forward movement. This is the basic balance strategy

RicB: Another thing as I'm thinking of this, eccentric allows the integration of the skeleton in a more effective way also. 
DM: Absolutely! - 11/17,8:24am; pg39
Lisamarie:
Quote:
Stretch reflex: muscle shortens to protect itself from an outside force. Opposite of golgi tendon reflex, which causes the muscle to relax. - 11/16, 5:44pm; pg37
*Question:
Don't understand this:
Quote:
MS: On skis it is possible and desirable in most cases, to start a new turn with some/all weight on the "lead" foot. Because that foot does not need to be moved. Right?

DM: OK, think about this. At the end/start of the turn COG is over the downhill ski. The new outside foot (which is uphill) is leading – just like in walking. How do you get COG over that foot? Hint. You don’t pull the foot back although many ski pros describe it that way. - 11/17, 4;21pm; pg44
let's use this picture as a reference:
http://www.ronlemaster.com/giantSlalom.htm
(take the 2nd one - of Lasse Kjus)

In the 5th frame you can see his COG is pretty much over the downhill (left and new inside) foot at the start of his left turn. Where (and Why?) would you want to get the COG over the outside foot? (In this case it would be the right foot) Don't you mean the outside foot is -supporting- the COG?
Or do you mean just before- at the end of his right turn-( in the 4th frame) the COG is over inside (right) foot which is soon to be the outside foot?

Relaxing/Stretch relflex:

Quote:
Thinking about pulling the foot back or tipping the ski on edge is way too much information when you are going 40-50 feet per second. Worse, it screws up your balance. In complex actitvities you get control by giving up control to your balance system. Reflex actions are tens of time faster than consciously mediated actions. 

Instead of tensing you have to work on learning the right position to turn on the stretch reflex and then relaxing. Less is more... - 11/18, 5:31pm; pg52
Quote:
What is especially important is the angle of the ankle joint that is present when the soleus changes to isometric contraction. If our ski posture is set up correctly (I will get to this) the forces of skiing will cause the soleus to revert to eccentric contraction in order to maintain this critical angle. Am I suggesting that consciously ‘flexing your ankle’ in skiing is a bad idea. Absolutely. - 11/19, 7:05am; pg52
*Can you elaborate on this? Why is it a bad idea to consciously 'flex your ankle'? More risk of injury?

does it have to do with this?:
Quote:
vail snopro:
For if we are not relaxed, and the muscles are already active, they can not do anything else until they do become relaxed. 
( This is a very common issue with recreational skiers- they do not understand that muscles can only do one thing at a time, then must be relaxed prior to their next operation. Instead, they try to go from one movement to another without relaxing, resulting in involving larger muscle groups to overcome the resistance of the original muscle. - 11/19, 1:59am; pg50
The inhibitory reflex:
Quote:
There’s a reflex in the body called the ‘inhibitory reflex’. It’s job is to prevent you from doing certain things until it has confirmed that the system responsible for performing the action is ready and especially, to ensure the resulting action is safe. - 11/20, 9:39pm; pg 62
Then the foot:
Quote:
In order to come up to power-up to a stable base of support the aches of the feet need to acquire both tension and stability against an opposing ground reaction force (GRF). - 11/20, 9:39pm; pg62
Quote:
the foot is still in the adaptive state. The supportive state is on standby awaiting confirmation by the inhibitory reflex that “the Eagle has landed”; i.e. that the foot is capable of supporting the body. How does it know when the foot is ready? The foot is ready to support the body when all 3 arches of the foot have found solid opposing resistance from the ground and the reflex is confident the application of force by COG will not destabilize the foot. Here we make one huge erroneous assumption; our ski boots, bindings and skis are the ground. - 11/20, 9:39pm; pg663
Here's the upshot for what needs to take place in the ski boot for a "conducive environment":
Quote:
“The human foot is one of the most dynamic organs in the human system”. 
Translation: The elements of the foot move with each other in 3 dimensional space against fixed references. And, by the way, they move significantly and continuously.

If we render the elements of the foot…..what is that word that boot fitters love to use? Ah yes, Stable then what? 
TRANSLATION: Make it undynamic – no movement – lock the sucker up. 
Is this a good thing? Probably not. It can not only greatly increase the effort required to ski it can decrease the effectiveness of the lower limb’s defense mechanism against injury from the interaction with the snow by up to 1000%

So the boot has to allow the elements of the foot to move between the space they are working at in two footed weight bearing (bipedal) and the space they are working at in one footed weight bearing (monopedal) under the maximal skiing loads. This means the lower boot shell or tub that your foot sits inside must have:
- Sufficient width for the maximal spread of your forefoot;
- Sufficient width for the maximal inward movement of your ankle bone and the structure of the midfoot, 
- Sufficient clearance for the soft tissue running along the inside of the foot between the ball of the foot and the midfoot, and
- Sufficient clearance for the movements for flexion of the ankle bone.

( plus this: 
One very important thing to add to the lower shell requirements:
- There must be room for the toes especially for the big toe to sit in its correct alignment which is straight ahead. 

The reason the toe box of the shell is a half circle has to do with the DIN binding standard. It has absolutely nothing whatsoever to do with the functional requirements of your foot. NOTHING -11/21, 9:55pm; pg 71 )

Why? So the foot can be fully loaded (compressed) in order to power-up its truss-like arch structure. If this doesn’t happen the skier does not have a strong foundation on which to construct a structural column on which to support COG and initiate eccentric contraction from. Pretty compelling reasons. We are only talking about the lower shell your foot sits in here. How about soft or stiff? If it has the right clearances you can make the shell out of steel if you want. Stiffness is not the issue. Clearance for the dynamic requirements of the foot is. 

SIDEBAR: What about the new ‘soft boots'. I have been there before the current crop hit the market. The challenge is to make the structure stable enough. Once you open the throat this is almost impossible. Would I ski in them? Are you kidding!
- 11/21, 8:55pm; pg69,70
The footbed issue:

Quote:
There are potentially very significant issues with anything your foot sits on the shell. These include the boot base or boot board and any kind of footbeds or orthotics. So far as I know I am the only party to have been involved in testing footbeds during actual skiing. At least 50% of those tested caused serious problems; they made you ski worse. While there are lots of opinions and theories as to why they are good, until their effect on the skier using them is proven with foot pressure data synced to video they are just that; opinions and unproven theories. - 11/21, 8:55pm; pg70
More on Footbeds/feet:
Quote:
I used to tell skiers “Don’t leave home without them”. I was the footbed God in our whole area. Most of the time the beds I made seemed to do some thing positive. Somet