CONTRIBUTION OF PHOSPHOCREATINE AND AEROBIC METABOLISM TO ENERGY SUPPLY DURING REPEATED SPRINT EXERCISE

This study examined the contribution of phosphocreatine (PCr) and aero bic metabolism during repeated bouts of sprint exercise. Eight male su bjects performed two cycle ergometer sprints separated by 4 min of rec overy during two separate main trials. Sprint I lasted 30 s during bot h main trials, whereas sprint 2 lasted either 10 or 30 s. Muscle biops ies were obtained at rest, immediately after the first 30-s sprint, af ter 3.8 min of recovery, and after the second 10- and 30-s sprints. At the end of sprint 1, PCr was 16.9 +/- 1.4% of the resting value, and muscle pH dropped to 6.69 +/- 0.02. After 3.8 min of recovery, muscle pH remained unchanged (6.80 +/-: 0.03), but PCr was resynthesized to 7 8.7 +/- 3.3% of the resting value. PCr during spl int 2 was almost com pletely utilized in the first 10 s and remained unchanged thereafter. High correlations were found between the percentage of PCr resynthesis and the percentage recovery of power output and pedaling speed during the initial 10 s of sprint 2 (r = 0.84, P < 0.05 and r = 0.91, P < 0. 01). The anaerobic ATP turnover, as calculated from changes in ATP,PCr , and lactate, was 235 +/- 9 mmol/kg dry muscle during the first sprin t but was decreased to 139 +/- 7 mmol/kg dry muscle during the second 30-s sprint, mainly as a result of a similar to 45% decrease in glycol ysis. Despite this similar to 41% reduction in anaerobic energy, the t otal work done during the second 30-s sprint was reduced by only simil ar to 18%. This mismatch between anaerobic energy release and power ou tput during sprint 2 was partly compensated for by an increased contri bution of aerobic metabolism, as calculated from the increase in oxyge n uptake during sprint 2 (2.68 +/- 0.10 vs. 3.17 +/- 0.13 l/min; sprin t 1 vs. sprint 2; P < 0.01). These data suggest that aerobic metabolis m provides a significant part (similar to 49%) of the energy during th e second sprint, whereas PCr availability is important for high power output during the initial 10 s.