Effects of concentric and eccentric exercise on protein catabolism in man

To test the effects of different modes of exercise on indices of protein catabolism, eight adult males on a meat-free diet performed single 60-min bouts of concentric and eccentric cycle ergometer exercise in two 7-day periods. Although the absolute intensities for the two exercise bouts were similar, VO2 averaged 70% and 40% of VO2 max for the concentric and eccentric exercise, respectively. Mean heart rate during the eccentric exercise was 26% lower (P less than 0.001) than during concentric exercise, and only for the latter was post-exercise lactate significantly elevated. The excretion of 3-methylhistidine, creatinine, and urea in 24 h urine samples was constant over the 2 weeks in which exercise was performed. Compared to pre-exercise values, the concentrations of 3-methylhistidine, creatinine, and urea were unchanged in serum samples obtained immediately after and for up to 48 h following eccentric exercise. However, serum urea concentration was elevated by 18% and 21% (P less than 0.05) in samples obtained immediately and 1 h after concentric exercise only. Despite the fact that the eccentric exercise was associated with delayed muscle soreness, these results reveal that neither concentric nor eccentric cycling exercise at moderate intensity had a major influence on indices of protein catabolism.