11. To demonstrate muscle fatigue, a student held an 8-lb dumbbell in her hand a
ID: 3521636 • Letter: 1
Question
11. To demonstrate muscle fatigue, a student held an 8-lb dumbbell in her hand and abducted her upper limb so that it was paralle tothe floor. After 45 seconds, she was having trouble holding that position, so she rotated her hand 90°. By doing so, she was able to hold te dumbbell in position for an additional 20 seconds. Which of the following statements best explains why the student could do that? a. The load was reduced. b. Different motor units were contracting while others were relaxing. c. The resistance to contraction was reduced d. Muscles began to contract isotonically rather than isometrically. e. The change in position provided a greater range of motion at the shoulderExplanation / Answer
The position mention above , the line of action of the force arm's weight is through the axis of rotation. During abduction of arm to the horizontal, the line of action is drawn farther away from the axis of rotation, so that,raising the force arm of the resistive torque. It is maximum at 90 degrees abduction. Beyond 90 degrees abduction, the line of action of the weight force again goes closer to the axis of rotation until at 180 degrees abduction, the force arm is 0 and no resistive torque exists.The student flex the elbow to bring the load closer to the axis of rotation , thus,reducing the force arm, and finally , the resistive torque.Ultimately the answer is the resistance to the contraction was reduced.
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