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.<|