Human muscle metabolism during intermittent maximal exercise

TLDR

High‑power 6‑s sprints rely equally on phosphocreatine breakdown and anaerobic glycolysis for energy. The study used ten 6‑s maximal cycle sprints with 30‑s recovery in eight men, sampling vastus lateralis muscle before and after the first sprint and just before and immediately after the tenth sprint. During the first sprint, phosphocreatine dropped 57% and lactate rose sharply, but in the tenth sprint lactate remained unchanged despite a 27% drop in power, indicating that the final sprint was supported mainly by phosphocreatine and aerobic metabolism rather than glycogenolysis.

Abstract

Eight male subjects volunteered to take part in this study. The exercise 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 sprint and 10 s before and immediately after the tenth sprint. The energy required to sustain the high mean power output (MPO) that was generated over the first 6-s sprint (870.0 +/- 159.2 W) was provided by an equal contribution from phosphocreatine (PCr) degradation and anaerobic glycolysis. Indeed, within the first 6-s bout of maximal exercise PCr concentration had fallen by 57% and muscle lactate concentration had increased to 28.6 mmol/kg dry wt, confirming significant glycolytic activity. However, in the tenth sprint there was no change in muscle lactate concentration even though MPO was reduced only to 73% of that generated in the first sprint. This reduced glycogenolysis occurred despite the high plasma epinephrine concentration of 5.1 +/- 1.5 nmol/l after sprint 9. In face of a considerable reduction in the contribution of anaerobic glycogenolysis to ATP production, it was suggested that, during the last sprint, power output was supported by energy that was mainly derived from PCr degradation and an increased aerobic metabolism.