Dynamics of anaerobic and aerobic energy supplies during sustained high intensity exercise on cycle ergometer

Eight male subjects were examined for the transition from anaerobic to aerobic energy supplies during supramaximal pedalling for 120 s on a cycle ergometer. The O2 debt and O2 deficit were measured for anaerobic supply, while O2 intake during exercise was measured for aerobic supply. The lactic acid system was also observed through postexercise peak blood lactate concentration [la-]b,peak. Since a continuous observation of O2 debt and [la-]b,peak during a single period of pedalling is not possible, pedalling of seven varying durations (5, 15, 30, 45, 60, 90 and 120 s) were repeated. Mechanical power output reached its peak immediately after the beginning of exercise, then rapidly declined, becoming gradual after 60 s. The O2 debt and O2 deficit were highest immediately after the beginning of exercise, then rapidly decreased to nil in 60 s. The O2 intake was small at the beginning, then rapidly increased to attain a steady state in 30 s at 80%-90% of the maximal O2 intake of the subject. Energy supply from the lactic acid system indicated by the increment in [la-]b,peak reached its highest value during the period between 5 and 15 s, then rapidly decreased to nil in 60 s. The results would suggest that anaerobic supply was the principal contributor during the initial stage of exercise, but that aerobic supply gradually took over. In 60 s anaerobic supply ceased, and aerobic supply became the principal contributor. The cessation of anaerobic energy supply took place much sooner than the 2 min that is conventionally suggested.