While watching Olympic weight lifters on television, Carl notices that on several occasions an athlete would lift the weight to his chest and then suddenly drop it. Can you offer an explanation for what might be happening?
What will be an ideal response?
What Carl is observing is an example of the stretch reflex in action. As the weight lifter lifts the weight, he is contracting the biceps brachii and brachialis muscles and at the same time stretching the triceps brachii muscle. If the mass is great, the amount of flexion necessary to move the mass could begin to overstretch the triceps that is being relaxed so as not to interfere with flexion. Stimulation of the muscle spindles in the triceps produces a reflex arc that brings about the relaxation of some of the motor units in the muscles involved in flexion, like the biceps. When the tension produced by the flexing muscles decreases to a point where they can no longer work against the resistance of the mass, the weight lifter will drop the weights involuntarily.
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