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Different plantar pressures in skiing

Discussion in 'Biomechanics, Sports and Foot orthoses' started by NewsBot, Jan 7, 2016.

  1. NewsBot

    NewsBot The Admin that posts the news.

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  2. NewsBot

    NewsBot The Admin that posts the news.

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  3. efuller

    efuller MVP

    The guy may know his skiiing, but he doesn't know his physics. We had the following discussion



     
  4. He wants to be "The Boss" of his own website, Eric. He will likely soon stop publishing your replies and your points about the inaccuracies of his statements.

    I did have to chuckle, though, when he told you to read Inman...... classic!.;)
     
  5. NewsBot

    NewsBot The Admin that posts the news.

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    NewsBot The Admin that posts the news.

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    NewsBot The Admin that posts the news.

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  8. Linchpin5

    Linchpin5 Member

    Postural responses utilize GRF. So where is the ground when the foot is on a platform with GRF on either the medial or lateral border? Let's start by framing the context in Newton's Laws. Then we can have the basis for a meaningful dialogue.
     
  9. efuller

    efuller MVP

    I'm not sure what you mean by postural responses.
    I'm not sure what you are asking "So where is the ground when the foot is on a platform... "

    I agree that this discussion should use Newton's Laws. A good place to apply them is in a free body diagram.

    Are you familiar with the concept of center of pressure? It is essentially the average point of force and Ground reaction force can be considered to be acting at the center of pressure.


    Linchpin5, are you related to the author of that piece that I quoted?

    Eric Fuller, DPM
     
  10. terigreen

    terigreen Active Member


    Ski Orthotics and Ski Biomechanics: The typical down hill skier's lower extremities never goes through a complete gait cycle. They ideally should have limited pedal mechanics between midstance and the beginning of propulsion, with the knee in flexion during the entire contact phase. When initiating a turn a skier will maintain their control by directing the downhill knee medially and transferring the load into the foot over the inside edge. This is done by internally rotating their tibia, causing a closed kinetic chain pronation of the foot, which transfers the pressure through the boot onto the ski edge. In ski boots subtalar joint supination and pronation are responding to knee function. With ski orthotics the goal is to control the knee function by supporting the foot anatomy. A custom heat moldable ski orthotic from Atlas Biomechanics, allow the skier to turn quicker and with more power. The skier will have a more efficient transfer of energy and will have decreased overall foot and knee fatigue. A ski orthotic from can make you a better skier. Teri Green, www.atlasbiomechanics.com
     
  11. NewsBot

    NewsBot The Admin that posts the news.

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  12. Linchpin5

    Linchpin5 Member

    Hello Eric, Please accept my apologies for the delay in responding to your comment. First off, I am one and the same as the author of the quoted piece. I started my blog in 2013 with the intent of stimulating objective discussion founded in principles of applied science. So your comments are appreciated

    In the context of skiing postural responses are CNS mediated responses to perturbations in GRF that tend to disrupt skier equilibrium.

    I am familiar with the concept of center of pressure as the point center of GRF. This assumes a contiguous source of GRF from ground or an extension of ground such as is present on the uppermost storey of 100 storey building where the foundations are ultimately founded on ground. However in ski maneuvers, the only time there is a contiguous source of GRF under the entire foot is at ski flat between edge change or when a skier is standing at a bar hoisting a few drinks acres ski. Although I have used the term COP in my blog posts, I am in the process of revising existing posts so indicate the load imposed by the weight of a skier as W. Here are two posts that are relevant to my posts currently listed.

    THE MECHANICS OF BALANCE ON THE OUTSIDE SKI: WHERE IS GROUND? - http://wp.me/p3vZhu-1V0
    THE MECHANICS OF BALANCE ON THE OUTSIDE SKI: TIMING OF EDGE CHANGE - http://wp.me/p3vZhu-1Y9
     
  13. efuller

    efuller MVP

    For example, the skier choosing to shift weight from one ski to the other. And many more.


    I have to disagree with your assertion that the only time there is contiguous source of ground reactive force is when the ski is flat and not on edge. There is a contiguous source of ground reactive force whenever the ski is in contact with the snow. When the ski is in the air there is no contiguous source. You can't make a turn in the air. You need to have force from the snow to make a turn. Newton's first law. objects stay at rest, or in constant motion in a straight line unless acted upon by an external force. If there is force acting on the ski, there will be a center of force.

    Eric
     
  14. efuller

    efuller MVP

    I realized I may have missed the crux of your point. I still disagree, but it comes down to this:

    Why do think Cop does not happen when the ski is on edge?

    Eric
     
  15. The use of center of pressure (CoP) does not assume a "contiguous source of GRF". Rather, CoP allows the summation of all reaction forces acting on the plantar foot or ski surface to be reconciled into a point location. Skiing on a ski edge still allows the CoP to be determined, just in a different location than when the ski if flat on the snow.
     
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