HUMAN MUSCLE METABOLISM DURING INTERMITTENT MAXIMAL EXERCISE

Eight male subjects volunteered to take part in this study. The exerci se protocol consisted of ten 6-s maximal sprints with 30 s of recovery between each sprint on a cycle ergometer. Needle biopsy samples were taken from the vastus lateralis muscle before and after the first spri nt and 10 s before and immediately after the tenth sprint. The energy required to sustain the high mean power output (MPO) that was generate d over the first 6-s sprint (870.0 +/- 159.2 W) was provided by an equ al contribution from phosphocreatine (PCr) degradation and anaerobic g lycolysis. Indeed, within the first 6-s bout of maximal exercise PCr c oncentration had fallen by 57% and muscle lactate concentration had in creased to 28.6 mmol/kg dry wt, confirming significant glycolytic acti vity. However, in the tenth sprint there was no change in muscle lacta te concentration even though MPO was reduced only to 73% of that gener ated in the first sprint. This reduced glycogenolysis occurred despite the high plasma epinephrine concentration of 5.1 +/- 1.5 nmol/I after sprint 9. In face of a considerable reduction in the contribution of anaerobic glycogenolysis to ATP production, it was suggested that, dur ing the last sprint, power output was supported by energy that was mai nly derived from PCr degradation and an increased aerobic metabolism.