THE EFFECTS OF STRETCH PARAMETERS ON ECCENTRIC EXERCISE-INDUCED DAMAGE TO TOAD SKELETAL-MUSCLE

Repeated contractions during which a muscle is stretched, known as ecc entric contractions, have previously been shown to produce damage. Thi s can be quantified by changes in various mechanical properties, of wh ich reduction in tension and a shift in the optimum length for tension generation to longer lengths are examined here. The magnitude of thes e changes has been reported to depend strongly on the number of stretc hes, the amplitude of each stretch and the maximum tension reached. On e proposed explanation of the changes predicts that muscle length shou ld have a strong influence, but past reports have been contradictory o n this point. Experiments were performed to test this hypothesis using whole toad sartorius muscles, which have the advantage of a relativel y small passive tension, allowing a large range of lengths to be used. Initial length, amplitude of stretch and number of eccentric contract ions were found by multiple linear regression to be the strong determi nants of changes due to eccentric exercise. Velocity had a weak effect , and tension, varied only by varying the length of maximally activate d muscles, was poorly correlated. (C) Chapman & Hall Ltd.