Human muscle metabolism during intermittent maximal exercise.
Level 4 - case-series / case-control
Single-group repeated-measures physiological study in healthy humans without a control group.
PubMed 8226473 · doi:10.1152/jappl.1993.75.2.712
What was done
Eight male volunteers performed ten 6-second maximal sprints on a cycle ergometer with 30 seconds of recovery between bouts. Vastus lateralis needle muscle biopsies were obtained before and immediately after the first sprint, as well as 10 seconds before and immediately after the tenth sprint, to assess phosphocreatine degradation and muscle lactate accumulation. Plasma epinephrine was measured after the ninth sprint, and mean power output was recorded.
What was found
Sprint 1 mean power output was 870.0 +/- 159.2 W, with energy supplied equally by phosphocreatine breakdown (muscle concentration fell by 57%) and anaerobic glycolysis (muscle lactate rose to 28.6 mmol/kg dry weight). By the tenth sprint, mean power output fell to 73% of sprint 1. Despite elevated plasma epinephrine (5.1 +/- 1.5 nmol/l after sprint 9), muscle lactate did not change during the tenth sprint, indicating an absence of net anaerobic glycogenolysis.
Why it matters
The study shows that during repeated brief maximal sprints, anaerobic glycolysis rapidly shuts down as an energy source, forcing the muscle to rely predominantly on phosphocreatine resynthesis and oxidative metabolism to maintain high power outputs.
Limits
The study is limited by a small sample size (n = 8) restricted to males. It lacks direct tissue measurements during intermediate sprints (sprints 2 through 9), and aerobic metabolism was inferred rather than directly quantified via continuous cellular oxygen consumption measurements.
Cited by
- partial After roughly 15 seconds of an all-out Wingate sprint test, muscle glycogen utilization largely shuts down due to extensive lactate accumulation and pH changes.