Effect of Stretch on Action Potential of Voluntary Muscle

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Abstract
The amplitude of the action potential recorded from various skeletal muscles of the frog, in response to a maximal motor nerve volley, is considerably greater in the stretched than in the unstretched muscle. This difference does not occur when the muscle is directly stimulated. Most of this stretch effect occurs near the "rest length" of the muscle. Prepns. which have been fatigued show a greater effect of stretch. Skeletal muscles of the rat and guinea pig usually do not exhibit this stretch effect, but may do so under certain conditions. The effect may be explained by assuming that not every muscle fiber necessarily responds to its motor nerve impulse in the unstretched muscle, but that such fibers may respond in the stretched muscle. This hypothesis is borne out by further evidence, given in the paper. With repetitive nerve volleys, at about 20/sec., the amplitude of the action potentials of the unstretched muscle rapidly builds up to a max. which is usually equal to the stable amplitude found in the stretched muscle. Temporal facilitation may, therefore, substitute for stretch facilitation. The possible significance of these findings for normal motor function is discussed.

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