Training induced adaptation of skeletal muscle and metabolism during submaximal exercise

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Abstract
Human subjects (6) were trained using a 1-leg bicycle exercise for 2 mo. The untrained leg served as control. After the training period, muscle oxidative capacity, determined as succinate dehydrogenase activity, was 27% higher in the trained (as opposed to the control) leg (P < 0.05). When the subjects in this situation performed a 1 h 2-legged submaximal bicycle exercise bout (150-225 W), determinations of .ovrhdot.VO2 of the single leg (leg blood flow .times. (A-V)O2 difference) revealed that they appeared to choose to work harder with their trained than with their untrained leg, so as to make the relative loads for the 2 legs the same. Determinations of O2 and CO2 on femoral arterial and venous blood demonstrated that the RQ was lower in the trained as compared to the untrained leg, 0.91 vs. 0.96 (10 min) and 0.91 vs. 0.94 (50 min) (P < 0.05). That metabolism of fat was more pronounced in the trained leg was further supported by the finding of a significant net uptake of free fatty acids in this leg only. A lower release of lactate from the trained leg was demonstrated. The shift towards a more pronounced metabolism of fat in the trained leg may be a function of an increased muscle oxidative capacity.