NO EVIDENCE OF OXIDANT STRESS DURING HIGH-INTENSITY ROWING TRAINING

In untrained subjects, strenuous exercise provokes the appearance of oxidant stress markers in blood and muscle. On the other hand, trained muscle is resistant to oxidant stress unless exercise challenges the muscle glycogen supply. It is not known whether chronic high-intensity exercise alters the susceptibility of skeletal muscle to oxidant stress, whether there are gender-related differences in markers of oxidant stress, or whether elevating muscle glycogen stores by increasing dietary carbohydrate can minimize any exercise-related oxidant stress. To address these issues, collegiate rowers (12 men, 11 women) were randomly assigned to a moderate-(MOD, 5 g/kg body wt) or high-carbohydrate (HI, 10 g/kg) diet in a double-blind design and underwent strenuous training for 4 wk. Training in the A.M. was 40 min at 70% maximal O2 consumption (VO2); in the P.M. it was either three 2,500-m time trials (to assess power output) or aerobic and lactate tolerance training. Total daily training time was 65 min at 70% maximal Vo, and 38 min at greater-than-or-equal-to 90% maximal VO2. Thrice-weekly morning blood samples were assayed for serum creatine kinase (CK), plasma thiobarbituric acid-reactive substances (TBARS), and serum beta-glucuronidase (beta-Gluc). Weekly muscle biopsies were obtained for analysis of glycogen and, when tissue sample quantity allowed, TBARS. HI rowers produced more power and improved power more (10.7 +/- 1.0 vs. 1.6 +/- 1.6%) over the 4 wk than did the MOD rowers. Preexercise muscle glycogen concentration was maintained at 119 mmol/kg in MOD but increased 65% in HI rowers (P < 0.05). Main effects, of time were observed for plasma TBARS, CK, and beta-Gluc (P < 0.05), but pairwise post hoc comparisons of means at different times were not significant. CK values averaged 55% lower in female than in male rowers (P < 0.05), but there were no gender-related. effects on the CK response to training. Sex-by-treatment interaction (P < 0.05) indicated that the plasma TBARS response was higher in the male HI rowers than in the other groups. It was concluded that the training caused no apparent oxidant stress/muscle damage and that both men and women rowers on either diet were able to adapt to the imposed training load.