Purpose: The assumption that the curvature constant (W[spacing acute]) of the power-duration relationship represents anaerobic work capacity is a controversial, unresolved question. We investigated if caffeine ingestion could increase total work done above critical power (CP), and if this would be accompanied by greater anaerobic energy expenditure and by an enhanced maintenance of maximal oxidative metabolic rate.
Methods: Nine men (26.6 +/- 5.3 years, V[spacing dot above]O2max 40.6 +/- 5.8 mL[middle dot]kg-1[middle dot]min-1) cycled until exhaustion at different exercise intensities on different days to determine the CP and W[spacing acute]. On separated days, participants cycled until exhaustion in the severe-intensity domain (136 +/- 7% of CP) after ingesting either caffeine (5 mg[middle dot]kg-1 body mass) or a placebo. Results
Time to exhaustion was 34% longer with caffeine compared to placebo, and this was accompanied by a greater work done above CP (23.7 +/- 5.7 vs 17.5 +/- 3.6 kJ; 130 +/- 30% vs 95 +/- 14% of W[spacing acute], P<0.01). Caffeine increased the aerobic energy expenditure (296.4 +/- 91.0 vs 210.2 +/- 71.9 kJ, P<0.01), but not anaerobic lactic, anaerobic alactic, and total anaerobic (lactic + alactic) energy expenditure. The end values of heart rate and ventilation were higher with caffeine, but the V[spacing dot above]O2 end was similar between conditions and was not different from V[spacing dot above]O2max. Caffeine did not change time to reach V[spacing dot above]O2max, but increased time maintained at V[spacing dot above]O2max (199.3 +/- 105.9 vs 111.9 +/- 87.1 s, P<0.05). Conclusions
Caffeine increased total work done above CP, but this was not associated with greater anaerobic work. Rather, this was associated with a higher tolerance to maintain exercise at maximal oxidative metabolic rate.
(C) 2017 American College of Sports Medicine