Experimental rapid sarcomere loss with concomitant hypoextensibility.

Slow soleus muscle in guinea pigs was actively shortened by constant electrical stimulation of the sciatic nerve for 12 hours. At the end of this period, hypoextensibility and a 25% decrease in the numbers of sarcomeres were observed. When a 36- or 48-hour period was allowed to elapse after the end of stimulation, some recovery occurred, and the sarcomere numbers were then found to be diminished by only 5%. If the stimulation was performed when the muscle was prevented from shortening (by ankle fixation in dorsiflexion), there was no decrease in sarcomere numbers and no hypoextensibility after neuroaxis lesions, when abnormal contractions maintain lasting shortening of the muscle.