Time-dependent effects of short-term training on muscle metabolism during the early phase of exercise

Green HJ, Bombardier E, Burnett ME, Smith IC, Tupling SM, Ranney DA. Time-dependent effects of short-term training on muscle metabolism during the early phase of exercise. Am J Physiol Regul Integr Comp Physiol 297: R1383-R1391, 2009. First published August 26, 2009; doi: 10.1152/ajpregu.00203.2009.-In this study, we investigated the hypothesis that the metabolic adaptations observed during steady-state exercise soon after the onset of training would be displayed during the nonsteady period of moderate exercise and would occur in the absence of increases in peak aerobic power ((V) over dotO(2peak)) and in muscle oxidative potential. Nine untrained males [age = 20.8 +/- 0.70 (SE) yr] performed a cycle task at 62% (V) over dotO(2peak) before (Pre-T) and after (Post-T) training for 2 h/day for 5 days at task intensity. Tissue samples extracted from the vastus lateralis at 0 min (before exercise) and at 10, 60, and 180 s of exercise, indicated that at Pre-T, reductions (P < 0.05) in phosphocreatine and increases (P < 0.05) in creatine, inorganic phosphate, calculated free ADP, and free AMP occurred at 60 and 180 s but not at 10 s. At Post-T, the concentrations of all metabolites were blunted (P < 0.05) at 60 s. Training also reduced (P < 0.05) the increase in lactate and the lactate-to-pyruvate ratio observed during exercise at Pre-T. These adaptations occurred in the absence of change in (V) over dotO(2peak) (47.8 +/- 1.7 vs. 49.2 +/- 1.7 ml . kg(-1) . min(-1)) and in the activities (mol . kg protein(-1) . h(-1)) of succinic dehydrogenase (3.48 +/- 0.21 vs. 3.77 +/- 0.35) and citrate synthase (7.48 +/- 0.61 vs. 8.52 +/- 0.65) but not cytochrome oxidase (70.8 +/- 5.1 vs. 79.6 +/- 6.6 U/g protein; P < 0.05). It is concluded that the tighter metabolic control observed following short-term training is initially expressed during the nonsteady state, probably as a result of increases in oxidative phosphorylation that is not dependent on changes in (V) over dotO(2peak) while the role of oxidative potential remains uncertain.