Comparison of the symptoms of exercise-induced muscle damage after an initial and repeated bout of plyometric exercise in men and boys

1 Cardiac Rehabilitation Department, Glan Clwyd Hospital, Rhyl; and 2 Children's Health and Exercise Research Centre, School of Sport and Health Sciences, University of Exeter, Exeter, United Kingdom Submitted 25 October 2004 ; accepted in final form 21 March 2005 The purpose of this study was to compare symptoms of exercise-induced muscle damage after an initial and repeated bout of plyometric exercise in men and boys. Ten boys (9–10 yr) and 10 men (20–29 yr) completed two bouts of eight sets of 10 plyometric jumps, 2 wk apart. Perceived soreness (0–10, visual analog scale), isometric strength of the quadriceps at six knee flexion angles, and countermovement jump and squat jump height were assessed before and at 30 min, 24 h, 48 h, and 72 h after each bout. All variables followed the expected patterns of change in men, with soreness peaking at 24–48 h (5.8 ± 1.7) and decrements in muscle function peaking at 30 min after the first bout (73–85% of baseline scores). Symptoms remained for 72 h after the first bout in men. In boys, symptoms were much less severe and peaked at 30 min (visual analog scale = 2.1 ± 1.8, functional decrements 87–92% of baseline) and, with the exception of soreness, returned to baseline after 24 h. After the second bout of plyometric exercise, the level of soreness and decrements in countermovement jump, squat jump, and isometric strength were lower, although the effect was stronger in men, in all cases. The results of this study suggest that although children may experience symptoms of muscle damage after intensive plyometric exercise, they are much less severe. A prior bout of plyometric exercise also appears to provide children with some protection from soreness after a subsequent bout of plyometric exercise. Explanations for milder symptoms of exercise-induced muscle damage in children include greater flexibility leading to less overextension of sarcomeres during eccentric exercise, fewer fast-twitch muscle fibers, and greater and perhaps more varied habitual physical activity patterns. repeated-bout effect; muscle function; children; flexibility; delayed-onset muscle soreness Address for reprint requests and other correspondence: R. G. Eston, Children's Health and Exercise Research Centre, School of Sport and Health Sciences, St. Luke's Campus, Univ. of Exeter, Exeter, UK, EX1 2LU (e-mail: r.g.eston{at}exeter.ac.uk )