FACTORS AFFECTING AMOUNT OF MUSCLE FORCE REQUIRED

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Muscles must produce a moment to match the moment that gravity produces at a joint: M_m=M_g Therefore: F_gs_g =F _ms_m

The muscle force (F_m) sufficient to balance this equation may change, depending on:

1. Changes in externally applied moment of force:

   While F_g doesn't change, its moment arm (s_g) does change throughout a movement task.

   Since the muscle must balance the moment which gravity produces, the force required of the muscle (F_m) changes.

2. Changes in the muscle's moment arm (s_m):

   If s_m changes through a joint's range of motion, the muscle must produce different levels of force (F_m) to maintain a constant moment.

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Last updated 9-15-00
Dave Thompson PT