Effects of short-term submaximal training in humans on muscle metabolism in exercise

Muscle metabolism, including the role of pyruvate dehydrogenase (PDH) in muscle lactate (Lac(-)) production, was examined during incremental exercise before and after 7 days of submaximal training on a cycle ergometer [2 h daily at 60% peak O-2 uptake ((V) over dot O-2max)]. Subjects were studied at rest and during continuous steady-state cycling at three stages (15 min each): 30, 65, and 75% of the pretraining (V) over dot O-2max. Blood was sampled from brachial artery and femoral vein, and leg blood flow was measured by thermodilution. Biopsies of the vastus lateralis were obtained at rest and during steady-state exercise at the end of each stage. (V) over dot O-2max leg O-2 uptake, and the maximum activities of citrate synthase and PDH were not altered by training; muscle glycogen concentration was higher. During rest and cycling at 30% (V) over dot O-2max, muscle Lac(-) concentration ([Lac-]) and leg efflux were similar. At 65% (V) over dot O-2max, muscle [Lac(-)] was lower (11.9 +/- 3.2 vs. 20.0 +/- 5.8 mmol/kg dry wt) and Lac(-) efflux was less [-0.22 +/- 0.24 (one leg) vs. 1.42 +/- 0.33 mmol/min] after training. Similarly at 75% (V) over dot O-2max, lower muscle [Lac(-)] (17.2 +/- 4.4 vs. 45.2 +/- 6.6 mmol/kg dry wt) accompanied less release (0.41 +/- 0.53 vs. 1.32 +/- 0.65 mmol/min) after training. PDH in its active form (PDHa) was not different between conditions. Calculated pyruvate production at 75% (V) over dot O-2max, fell by 33%, pyruvate reduction to lactate fell by 59%, and pyruvate oxidation fell by 24% compared with before training. Muscle contents of coenzyme A and phosphocreatine were higher during exercise after training. Lower muscle lactate production after training resulted from improved matching of glycolytic and PDHa fluxes, independently of changes in muscle O-2 consumption, and was associated with greater phosphorylation potential.