PROTECTIVE EFFECT BY SHORT MUSCLE LENGTH ECCENTRIC EXERCISE ON LONG MUSCLE LENGTH ECCENTRIC EXERCISE

A first bout of eccentric exercise attenuates muscle damage from subsequent bouts of the same exercise. It has been shown that eccentric actions at a long muscle length (L-ECC) result in greater development of muscle damage compared to those at a short muscle length (S-ECC), with only brachialis being damaged by S-ECC, whereas L-ECC also damages biceps brachii. The purpose of this study was to investigate the hypothesis that a first bout of eccentric exercise in which S-ECC was performed could partially attenuate muscle damage by a second bout in which L-ECC was performed. Twelve male students performed 24 maximal eccentric actions of the elbow flexors over an elbow joint angle of 0.87 to 1.74 rad (50–100°: S-ECC) followed 4 weeks later by eccentric actions across an elbow joint angle from 2.27 to 3.14 rad (130–180°: L-ECC). Another group of subjects (n = 11) performed L-ECC in both the first and second bouts. Changes in maximal isometric force, range of motion, upper arm circumference, muscle soreness, plasma creatine kinase activity, and ultrasound and magnetic resonance images were compared between the bouts and groups. All measures changed significantly (P < 0.01) after S-ECC and L-ECC for the first bout, however significantly (P < 0.01) larger changes in the measures were found in L-ECC compared to S-ECC. The second bout resulted in significantly (P < 0.05) smaller changes in all criterion measures than the first bout for both groups, but the magnitude of the protective effect was significantly (P < 0.05) larger for the groups performed L-ECC for the first bout. These results suggest that eccentric exercise at a short muscle length is effective in preventing severe muscle damage caused by eccentric exercise at a long muscle length.