Immediate effects of stretch on muscle contractility

¹ Department of Physiology, Albany Medical College, Albany, New York

A study has been made of changes in the contractile response in striated muscle (isolated frog gastrocnemius) and smooth muscle (puppy bladder in situ) during the stress relaxation which follows sudden stretch. In both types of muscle, there is a progressive increase in the peak contractile response as partial decay of the stretched resting tension occurs. With large stretches of striated muscle and with any significant stretch of smooth muscle, this phenomenon is followed by a further decay in resting tension without alteration in the magnitude of the contractile response. Immediately after sudden stretch, there is a brief period during which the contractile response may be reduced. These results are interpreted in the light of theoretical muscle models, and it is emphasized that part of the stress relaxation process appears to involve the lengthening of shortened contractile links so that they become actively contractile.