Caffeine improves supramaximal cycling but not the rate of anaerobic energy release

The purpose of this study was to determine if improved supramaximal exercise performance in trained cyclists following caffeine ingestion was associated with enhanced O(2) uptake ((V) over dotO(2) kinetics), increased anaerobic energy provision (accumulated O(2)-AO(2)-deficit), or a reduction in the accumulation of metabolites (for example, K(+)) associated with muscular fatigue. Six highly trained male cyclists ((V) over dotO(2)peak 68 +/- 8 mL kg(-1) min(-1)) performed supramaximal (120% (V) over dotO(2)peak) exercise bouts to exhaustion on an electronically braked cycle ergometer, following double-blind and randomized ingestion of caffeine/placebo (5 mg kg(-1)). Time to exhaustion (TE), (V) over dotO(2) kinetics, AO(2) deficit, blood lactate (La(-)), plasma potassium (K(+)), caffeine and paraxanthine concentrations were measured. Caffeine ingestion elicited significant increases in TE (14.8%, p < 0.01) and AO(2) deficit (6.5%, p < 0.05). In contrast, no changes were observed in AO(2) deficit at isotime, (V) over dotO(2) kinetics, blood [La(-)] at exhaustion or peak [K(+)] following caffeine ingestion. However, [K(+)] was significantly reduced (13.4%, p < 0.01) during warm-up cycling immediately prior to the onset of the supramaximal bout for the caffeine trials, compared with placebo. It appears that caffeine ingestion is beneficial to supramaximal cycling performance in highly trained men. The reduced plasma [K(+)] during submaximal warm-up cycling may prolong the time taken to reach critical [K(+)] at exhaustion, thus delaying fatigue. Considering caffeine ingestion did not change (V) over dotO(2) kinetics or isotime AO(2) deficit, increases in absolute AO(2) deficit may be a consequence of prolonged TE, rather than causal.