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 exerc ise, 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 rap idly extracted from vastus lateralis indicated reductions (p < 0.05) o f 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 an d 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 resu lts suggest that at least part of the tightening of the metabolic cont rol and the apparent reduction in glycogenolysis and glycolysis in res ponse to short-term training occurs during the adjustment phase to ste ady-state exercise.