The effects of stretch parameters on eccentric exercise-induced damage to toad skeletal muscle.

Repeated contractions during which a muscle is stretched, known as eccentric contractions, have previously been shown to produce damage. This can be quantified by changes in various mechanical properties, of which reduction in tension and a shift in the optimum length for tension generation to longer lengths are examined here. The magnitude of these changes has been reported to depend strongly on the number of stretches, the amplitude of each stretch and the maximum tension reached. One proposed explanation of the changes predicts that muscle length should have a strong influence, but past reports have been contradictory on this point. Experiments were performed to test this hypothesis using whole toad sartorius muscles, which have the advantage of a relatively small passive tension, allowing a large range of lengths to be used. Initial length, amplitude of stretch and number of eccentric contractions were found by multiple linear regression to be the strong determinants of changes due to eccentric exercise. Velocity had a weak effect, and tension, varied only by varying the length of maximally activated muscles, was poorly correlated.