MYOCELLULAR ENZYME LEAKAGE, POLYMORPHONUCLEAR NEUTROPHIL ACTIVATION AND DELAYED-ONSET MUSCLE SORENESS INDUCED BY ISOKINETIC ECCENTRIC EXERCISE

To address the question of whether delayed onset muscular soreness (DO MS) following intense eccentric muscle contraction could be due to inc reased production of the arachidonic acid derived product prostaglandi n E(2) (PGE(2)), 10 healthy male subjects were submitted to eccentric and concentric isokinetic exercises on a Kin Trex device at 60 degrees /s angular velocity. Exercise consisted of 8 stages of 5 maximal contr actions of the knee extensor and flexor muscle groups of both legs sep arated by 1 min rest phases. There was an interval of at least 30 days between eccentric and concentric testing, and the order of the two ex ercise sessions was randomly assigned. The subjective presence and int ensity of DOMS was evaluated using a visual analogue scale, immediatel y, following 24 h and 48 h after each test. Five blood samples were dr awn from an antecubital vein: at rest before exercise, immediately aft er, after 30 min recovery, 24 h and 48 h after the tests. The magnitud e of the acute inflammatory response to exercise was assessed by measu ring plasma levels of polymorphonuclear elastase ([EL]), myeloperoxida se ([MPO]) and PGE(2) ([PGE(2)]). Using two way analysis of variance, it appeared that only eccentric exercise significantly increased [EL] and DOMS, especially of the hamstring muscles. Furthermore, a signific ant decrease in eccentric peak torque of this muscle group only was ob served on day 3 after eccentric work (-21%; P <0.002). Serum activity of creatine kinase and serum concentration of myoglobin increased sign ificantly 24 and 48 h after both exercise tests. Mean [PGE(2)] in the two exercise modes remained unchanged over time and were practically e qual at each time point. On the basis of these findings, we conclude t hat the magnitude of polymorphonuclear (PMN) activation, muscle damage , and DOMS are greater after eccentric than after concentric muscle co ntractions. However, the hypothesized interplay between muscle damage, increased PGE(2) production, DOMS sensations, and reduced isokinetic muscle performance was not substantiated by the present results.