Effect of intermittent eccentric contractions on symptoms of muscle microinjury.

The purpose was to determine whether varying the duration of rest between contractions affects selected symptoms of eccentric contraction-induced skeletal muscle microinjury. Thirty-three women were assigned to three groups (N = 11). Each performed one bout of exercise with each arm involving 10 eccentric contractions of the elbow flexor muscles, lowering a load equaling 60% of maximal static force. One arm exercised continuously; the other exercised with rest periods of 15 s, 5 min, or 10 min between contractions, depending on the group. Preexercise and 0, 24, and 48 h postexercise, symptoms of microinjury in the elbow flexor muscles were assessed: soreness and changes in strength, resting elbow angle ("musculotendinous stiffness"), and arm girth ("swelling"). For all groups combined, 10 continuous contractions caused changes (P < 0.05) in all variables at every measurement time. For example, soreness ratings (0-10 scale) were 4.3 +/- 2.0 (24 h) and 4.3 +/- 2.1 (48 h) and strength was reduced 18% 0 h postexercise. Responses were similar with 15 s of rest between contractions. Although they were moderated, symptoms occurred even with 5 and 10 min of rest. With 10 min between contractions, soreness occurred (e.g., 2.4 +/- 1.5 [24 h]) and strength was 17% reduced 0 h postexercise. Results are most consistent with a mechanical cause of eccentric contraction-induced muscle microinjury, rather than a metabolic or other factor with a short recovery time, although involvement of the latter cannot be ruled out.