No announcement yet.

Re: (Fwd) body instability under load

This topic is closed.
  • Filter
  • Time
  • Show
Clear All
new posts

  • Re: (Fwd) body instability under load

    I would recheck your assumption that the body is failing or
    fatiguing under compression. The body geometry the lifter is in is a
    fairly stable position. The "shaking" you are observing is what is
    sometimes called "muscle load shearing" though there are more technical
    terms. I believe what you are observing are muscles adjacent to each
    other trading off. This is something your body does to avoid fatigue.
    The lifter, however, is pretty much maxing out the majority of his
    muscles so it appears that he is actually shaking. You may also be
    observing antagonist muscles trying to hold an unstable equilibrium point
    (since the weight is high over head and must be maintained is a special
    spot); if you really want to investigate this phenomenon(sp?) from a
    MechEngr view point, I would suggest you begin your research with a
    review of inverted pendulum control work. The lifter is not shaking
    "uncontrollably", rather his body is executing an inverted pendulum
    control that is fairly unstable due to the dynamic fatiguing of the muscles.

    hope this helps
    john smith
    university of illinois

    On Fri, 28 Jul 1995, Mr A G S Hofmeyr wrote:

    > Forwarded message:
    > From: Self
    > To:
    > Subject: body instability under load
    > Date: Fri, 28 Jul 1995 14:11:31
    > In the weightlifting Clean and Jerk the weightlifter is required to
    > hold the weight steady overhead to succesfully complete the lift.
    > It has been observed that when a world record weight is held overhead
    > thelifter tends to shake uncontrollably.
    > The body has to support the weight in compression and there is a
    > limiting weight that any structure can support in compression. At
    > this limiting or buckling weight the stiffness of the structure is
    > reduced to zero hence the inability to stop lateral movement.
    > It is proposed to develop a theoretical model of the body as
    > a structure under compression with the correct geometry and spring
    > stiffnesses.
    > Has anyone worked on this topic?