Metabolic adaptations to short-term training are expressed early in submaximal exercise

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Abstract
In previous studies we have been able to demonstrate tighter metabolic control of muscle metabolism during prolonged steady-state exercise 5 to 6 days after the initiation of training and well before changes in oxidative potential. To examine whether the metabolic adaptations are manifested during the non-steady-state adjustment to submaximal exercise, 11 male subjects (Vo2 peak, 45 +/- 2.4 mL.kg(-1). min(-1), X +/- SE) performed 98 min of cycle exercise at 67% of Vo2 peak prior to and following 3 to 4 days of training for 2 h per day. Analysis of lactate concentration (mmol/kg dry weight) in samples rapidly extracted from vastus lateralis indicated reductions (p < 0.05) of 44% at 3 min ( 42.1 +/- 7.1 vs. 23.6 +/- 7.7), 29% at 15 min (35.4 +/- 6.4 vs. 25.0 +/- 6.0), and 32% at 98 min (22.9 +/- 6.9 vs. 15.6 +/- 3.2) with training. Training also resulted in higher phosphocreatine and lower creatine and P(i) values that were not specific to any exercise time point. In addition, Vo2 was not altered either during the non-steady state or during the steady-state phases of exercise. These results suggest that at least part of the tightening of the metabolic control and the apparent reduction in glycogenolysis and glycolysis in response to short-term training occurs during the adjustment phase to steady-state exercise.