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Bodybuilder “Hulk” Heise is doing leg curls on a Cybex machine. “Hulk” gets stuck (see figure) with 90° angle at the knee joint. The force exerted by the machines (FA) on his leg is 500 N, directed at an angle of 55° (angle α) relative to the tibia, and the distance from “Hulk’s” knee joint to the point where the force is being applied is 55 cm (distance L). For this problem, assume the weight of the shank and foot is negligible and the muscle force (FM) acts perpendicular to the tibia in this position.
a. What is the length of the moment arm from the knee joint to the applied force (FA)? (hint: drawing a line and use trigonometry will help)
__________
b. What is the torque created by the applied force (FA), about the knee joint? __________
c. After finding the torque above, how much force is required from the hamstrings (FM) to balance or offset the extension torque created by the applied force (FA) (note: moment arm for the line of action of hamstring is given)
__________
d. Which lever is this exercise applied to (circle one)
1st lever 2nd lever 3rd lever
a. What is the length of the moment arm from the knee joint to the applied force (FA)? (hint: drawing a line and use trigonometry will help)
__________
b. What is the torque created by the applied force (FA), about the knee joint? __________
c. After finding the torque above, how much force is required from the hamstrings (FM) to balance or offset the extension torque created by the applied force (FA) (note: moment arm for the line of action of hamstring is given)
__________
d. Which lever is this exercise applied to (circle one)
1st lever 2nd lever 3rd lever
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