The effects of concentric and eccentric exercise performed at long muscle length on muscle damage.

This study aimed to examine the effects of contraction type (concentric vs. eccentric) on exercise-induced muscle damage when performed at long muscle length. Thirteen female participants performed maximal voluntary intensity isokinetic concentric and eccentric exercise using their elbow flexors on an isokinetic dynamometer, each assigned to a randomly selected arm. The exercise protocols consisted of 75 repetitions at long muscle length [range of motion: 5°-50° (0° full extension)]. Muscle damage indices and ultrasonographic parameters were assessed before and at 24-, 48-, 72-, and 96 h post-exercise. No significant exercise type by time interaction and main effect of exercise type was observed for any of the studied parameters (p = 0.097-0.873). A significant main effect of time was found in isometric peak torque, ROM, DOMS, muscle thickness, and echo intensity of both biceps brachii and brachialis (i.e. p < 0.01 for all parameters). Isometric peak torque and ROM decreased significantly at 24 h post eccentric exercise (p < 0.05). DOMS and muscle thickness significantly increased after both exercise types (p < 0.001), while echo intensity changed significantly only after eccentric exercise (p < 0.001). These results suggest that unfamiliar isokinetic exercise at long muscle lengths can induce muscle damage, independent of contraction type.