Question

A person in a prone position wants to do a leg curl with the shank starting from a horizontal orientation. The COG of the 36 N shank & foot is 0.30 m from the knee and the 445 N weight is 0.50 m from the knee. If the hamstrings are inserted 0.075 m from the knee, how much vertical muscle force is needed to move the weight upward? If the muscle is pulling at a 15º angle with the shank, how much resultant muscle force is necessary to move the weight upward?

Answer 1

Muscle force is acting vertially upward. Forces acting at the knee joint are ,horizontally to right and vertically up.

Net torque about the knee joint is zero,

Vertical muscle force needed is

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If the muscle is at an angle to the shank,

Net torque about the knee joint is zero,

Resultant muscle force needed is

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