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)
|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
|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
|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
Don't understand this:
|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?
|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
|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?:
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:
|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:
|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
|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":
|“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:
|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:
|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. - 11/22, 7:23am; pg73
* I'm pretty sure I have a loose arch (dammit!) -no wonder getting boots is such a PIA. A vacuum formed footbed is not the answer?
|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.
- 11/22, 8:40am; pg 74
|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?
-11/22, 4:09pm; pg 80
* So how are you supposed to flex if not by releasing and letting your shin go forward?
|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.
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 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. ...What is the best way to fit most liners?? In the garbage can. 11/22, 5:11pm; pg 80
|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. 11/22, 7:17pm; pg 82
*So what's the problem with the liners? Too much pressure? How are you supposed to keep the foot/shin tight so you have control and yet "free" so the foot can adapt to balance? Also, I take it you don't like the Booster Strap that keeps the cuff against the shin but is elastic? Or is it o.k. if the tongue contacts the shin all the time as long as the tongue doesn't contact the boot?
|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 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
11/23, 5:16pm; pg 85
Here's the explanation:
|The idea (was?) to make it easy to understand that as the cuff resistance increased the muscle contribution to the equation would eventually reach zero. In other words either soleus can equal the external force or the external force of the cuff shaft can equal the external force or there will be a mixture of the 2. 11/24,3:51pm; pg 93
* So again, how are you suppossed to apply forward pressure to the boot? You've said elsewhere that forward stiffness is not an issue. How is this possible?[ November 26, 2002, 12:09 PM: Message edited by: Tog ]