Stretch reduces central core lesions and calcium build-up in tenotomized soleus

The incidence of skeletal muscle tendon rupture is increasing. The unloaded, shortened muscle undergoes rapid degeneration. Rehabilitation takes 10-12 weeks and includes stretch therapy. Outcomes may be improved by understanding the pathophysiological changes and stretch mechanisms. We investigated the effects of passive stretch on preventing central core lesions in a rat tenotomy model of simulated Achilles tendon rupture. Adult male rats were tenotomized bilaterally. At 7 days, 39% of the soleus fibers possessed central core lesions. Whole muscle calcium concentration progressively increased and plateaued by 4 days. Dantrolene, a calcium release blocker, injected daily for 7 days, reduced central core lesion formation and calcium build-up. Passive stretch, 20 min/day, inhibited central core lesion formation. Calcium increased at 4 days in mitochondria, and stretch prevented this increase. These findings indicate that stretch therapy reduces central core lesion occurrence by preventing calcium elevation in hypershortened muscles.