Severity of contraction-induced injury is affected by velocity only during stretches of large strain.

Our purpose was to investigate the effect of velocity of stretch on contraction-induced injury to whole skeletal muscles. Single stretches provide an effective method for studying factors that initiate contraction-induced injury. We tested the null hypothesis that the severity of injury is not dependent on the velocity of the stretch. From the plateau of maximum isometric contractions, extensor digitorum longus muscles of mice were administered single stretches in situ of 30--50% strain relative to muscle fiber length (L(f)) at rates of 1--16 L(f)/s. The magnitude of injury was represented by the isometric force deficit 1--10 min after the stretch. Although the null hypothesis was not supported because the force deficit was affected by velocity (r(2) = 0.09), the effect was relatively weak and was not significant except at the largest strain. Velocity had no effect on peak or average force or work input, factors established to have significant relationships with the force deficit. Velocity may play a minor role in contraction-induced injury, but its importance is negligible relative to that of strain.