METABOLIC ADAPTATIONS TO SHORT-TERM TRAINING ARE EXPRESSED EARLY IN SUBMAXIMAL EXERCISE

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 (Vo(2) peak, 45 +/- 2.4 mL . kg(-1). min(-1), ($) over bar X +/- SE) performed 98 min of cycle exercise at 67% of Vo(2) 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, Vo(2) 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.