EFFECTS OF ENDURANCE TRAINING ON SKELETAL-MUSCLE OXIDATIVE CAPACITIESWITH AND WITHOUT SELENIUM SUPPLEMENTATION

The purpose of this study was to examine the changes induced by endura nce training, with or without selenium (Se) supplementation on: 1) mit ochondrial activity of succinate dehydrogenase (SDH) and cytochrome c oxidase (Cyt Ox), 2) the myosin heavy chain (MHC) expression in muscle fibers and 3) their association with aerobic performance. Twenty-four male students volunteered to participate in this double blind study: selenium (Sel, N = 12) vs placebo (Pla, N = 12). During a IO-wk endura nce training program, the Sel group received a daily Se supplementatio n containing 180 mu g of organic selenium (selenomethionine), while th e Pla group received a placebo. Before (Pre) and after (Post) the prog ram (3 sessions wk(-1)) an endurance exercise (Cap(max)) was performed in order to determine the aerobic endurance capacity assessed by the total oxygen uptake during the running test (VO2tot). All parameters o f aerobic performance were increased in both groups, concomitantly to a rise in mitochondrial Cyt Ox activity. Two positive relationships we re found: 1) between type I MHC and VO2tot increments (r = 0.65, P < 0 .05), 2) between training volumes and VO2tot increments (r = 0.53, P < 0.05; N = 23). The training program produced an 8.2% significant incr ease in type I MHC (P < 0.05) while type II MHC decrease was not signi ficant (-4.4%). Although they were almost non-existant before the prog ram, muscle fibers which co-expressed type I and II MHC displayed a ma rked increase afterwards (4.9 +/- 5.7 vs 1.1 +/- 2.1%, P < 0.05). Musc le GSH-Px activity, at rest, did not respond to endurance training or Se supplementation. The results suggest that the neuromuscular system is still in an evolutive state after 10 weeks of endurance training, a nd that selenium supplementation has no effect on endurance training-i nduced adaptations.