Initial aerobic power does not alter muscle metabolic adaptations to short-term training.
To investigate the hypothesis that training-induced increases in muscle mitochondrial potential are not obligatory to metabolic adaptations observed during submaximal exercise, regardless of peak aerobic power (VO(2 peak)) of the subjects, a short-term training study was utilized. Two groups of untrained male subjects (n = 7/group), one with a high (HI) and the other with a low (LO) VO(2 peak) (means +/- SE; 51.4 +/- 0.90 vs. 41.0 +/- 1.3 ml. kg(-1). min(-1);P < 0.05), cycled for 2 h/day at 66-69% of VO(2 peak) for 6 days. Muscle tissue was extracted from vastus lateralis at 0, 3, and 30 min of standardized cycle exercise before training (0 days) and after 3 and 6 days of training and analyzed for metabolic and enzymatic changes. During exercise after 3 days of training in the combined HI + LO group, higher (P < 0.05) concentrations (mmol/kg dry wt) of phosphocreatine (40.5 +/- 3.4 vs. 52.2 +/- 4.2) and lower (P < 0.05) concentrations of P(i) (61.5 +/- 4.4 vs. 53.3 +/- 4.4), inosine monophosphate (0.520 +/- 0.19 vs. 0.151 +/- 0.05), and lactate (37.9 +/- 5.5 vs. 22.8 +/- 4.8) were observed. These changes were also accompanied by reduced levels of calculated free ADP, AMP, and P(i). All adaptations were fully expressed by 3 min of exercise and by 3 days of training and were independent of initial VO(2 peak) levels. Moreover, maximal activity of citrate synthase, a measure of mitochondrial capacity, was only increased with 6 days of training (5.71 +/- 0.29 vs. 7.18 +/- 0.37 mol. kg protein(-1). h(-1); P < 0. 05). These results demonstrate that metabolic adaptations to prolonged exercise occur within the first 3 days of training and during the non-steady-state period. Moreover, neither time course nor magnitude of metabolic adaptations appears to depend on increases in mitochondrial potential or on initial aerobic power.
Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.
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Green
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Grant
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Bombardier
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Ranney
D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D002950:Citrate (si)-Synthase / Q000378:metabolism; D004734:Energy Metabolism / Q000502:physiology; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D010710:Phosphates / Q000378:metabolism; D010806:Physical Education and Training; D010807:Physical Endurance / Q000502:physiology; D013385:Succinate Dehydrogenase / Q000378:metabolism; D013997:Time Factors
D010710:Phosphates; D013385:Succinate Dehydrogenase; D002950:Citrate (si)-Synthase