Movement: Lecture 9/10 part 2

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  1. Muscles generally develop forces sufficient to maintain:
    a rotational equilibrium around a joint
  2. We assume that mm act to oppose:
    gravity
  3. Rotational equlibrium=
    the sum of all the moments that act around a joint's axis is equal to zero
  4. All the adductor moments are balanced by:
    equal and opposite abductor moments
  5. Mm+Mg=
    0
  6. moments:
    products of forces
  7. moment=
    force x distance
  8. When do we encounter disequilibrium?
    we don't always activate mm to counter the effects of gravity. Sometimes, we move in such a way that gravity assists our movements, as when we throw a ball from a height, or slam a book downward on the table
  9. Muscles generally develop forces sufficient to maintain:
    a rotational equilibrium around a joint
  10. What are the 3 assumptions of gravity and muscle wars?
    • the opposing moments are exactly equal
    • the mm produce a moment that exceeds the moment which gravity produces
    • the mm produce moment that opposes the effect of gravity but is nevertheless smaller than moment that gravity produces
  11. Mm=Mg
    • joint doesn't move so muscle's length remains constant
    • isometric muscle action
  12. Mm>Mg
    joint moves as muscle shortens in concentric action
  13. Mm<Mg
    joint moves in direction dictated by gravity's moment. while muscle's activity exerts force on attachments, and controls gravity's effect on joint, muscle still elongates. Eccentric muscle action
  14. Factors affecting the amount of muscle force required:
    • muscles must produce a moment to match the moment that gravity produces at a joint
    • Mm=Mg
    • Therefore:
    • Fgsg=Fmsm
  15. Factors affecting the amount of muscle force required:
    the muscle force sufficient to balance this equation may change depending on:
  16. 1. Changes in externally applied moment of force:
    while Fg doesn't change, its moment arm does change throughout a movement task
    since the muscle must balance the moment which gravity produces, the force required of the muscle changes
    • 2. Changes in the muscle's moment arm: if sm changes through a joint's range of motion, the muscle must produce different levels of force to maintain a constant moment
    • if the muscle's moment arm increases anywhere in the range of motion, the muscle can produce less force and still produce the same moment around the joint
    • if the muscle's moment arm decreases, it must develop additional force to maintain the same moment

Card Set Information

Author:
 brau2308
ID:
 171604
Filename:
 Movement: Lecture 9/10 part 2
Updated:
 2012-09-18 03:34:54
Tags:
human movement
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Description:
review of human movement lecture 9/10 part 2
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