Muscle metabolic, enzymatic and transporter responses to a session of prolonged cycling.

A single session of prolonged work was employed to investigate changes in selected metabolic, transporter and enzymatic properties in muscle. Ten active but untrained volunteers (weight = 73.9 ± 4.2 kg) with a peak aerobic power [Formula: see text] of 2.95 ± 0.27 l min(-1), cycled for 2 h at 62 ± 1.3% [Formula: see text] Tissue extraction from the vastus lateralis occurred prior to (E1-Pre) and following (E1-Post) exercise and on 3 consecutive days of recovery (R1, R2, R3). The exercise resulted in decreases (P < 0.05) in ATP (-9.3%) and creatine phosphate (-49%) and increases in lactate (+100%), calculated free ADP (+253%) and free AMP (+1,207%), all of which recovered to E1-Pre by R1. Glycogen concentration, which was depressed (P < 0.05) by 75% at E1-Post, did not recover until R3. Compared to E1-Pre, the cycling also resulted in decreases (P < 0.05) in the activities of cytochrome c oxidase, phosphorylase, and hexokinase but not in citrate synthase (CS) or 3-hydroxy-CoA dehydrogenase at E1-Post. With the exception of CS, which was elevated (P < 0.05) at R3, all enzyme activities were not different from E1-Pre during recovery. For the glucose (GLUT1, GLUT4) and monocarboxylate (MCT1, MCT4) transporters, changes in expression levels (P < 0.05) were only observed for GLUT1 at R1 (+42%) and R3 (+33%). It is concluded that the metabolic stress produced by prolonged exercise is reversed by 1 day of recovery. One day of exercise also resulted in a potential upregulation in the citric acid cycle and glucose transport capabilities, adaptations which are expressed at variable recovery durations.