A ten-pound weight is held so that it can be moved in either direction by the biceps and triceps (e.g. arm abducted with flexion and extension in the horizontal plane). How much effort will the triceps need as compared to the biceps where the effort arm is 1 inch for the triceps and 2 inches for the biceps? The weight is held in the hand at a point 12 inches from the elbow.

Question

Quizplus · Accepted Answer

According to the principle of torque, the effort needed by the triceps and biceps can be calculated as follows:

Torque = Force x Effort arm

For the biceps, the torque required to lift the weight is:

10 lbs x 2 inches = 20 lb-inches

For the triceps, the effort arm is half that of the biceps, so the torque required is:

10 lbs x 1 inch = 10 lb-inches

Therefore, the triceps need half as much effort as the biceps to lift the weight, or two times less effort. Hence, the correct answer is B) triceps 2 times as much as biceps.

A Ten-Pound Weight Is Held So That It Can Be