Exercise-induced muscle damage, repair, and adaptation in humans.

This study examined exercise-induced muscle damage, repair, and rapid adaptation. Eight college-age women performed three eccentric exercises of the forearm flexors. One arm performed 70 maximal contractions (70-MAX condition), and the other arm performed 24 maximal contractions (24-MAX) followed 2 wk later by 70 maximal contractions (70-MAX2). Criterion measures of serum creatine kinase, muscle soreness and pain, isometric strength, and muscle shortening were assessed before, immediately after, and for 5 days after each exercise. Significant changes in all criterion measures were found after the 70-MAX exercise with a slow recovery that was not complete by day 5 after exercise. The 24-MAX condition showed only small changes in the criterion measures. Changes in the criterion measures after the 70-MAX2 exercise were significantly smaller than those after the 70-MAX exercise. Results from this study, with regard to the ability of the muscle to adapt to exercise-induced damage, suggest that an adaptation takes place such that the muscle is more resistant to damage and any damage that does occur is repaired at a faster rate. It is also clear that a relatively small insult will produce this adaptation.