Purpose: This study investigated the effects of a low and moderate caffeine dose on exogenous CHO oxidation and endurance-exercise performance. Methods: Nine trained and familiarized male cyclists (mean ± SD: 29.4 ± 4.5 yr, 81.3 ± 10.8 kg body weight [BW], 183.8 ± 8.2 cm, VO2peak = 61.7 ± 4.8 mL/kg·min) undertook three trials, with training and high CHO diet being controlled. One hour before exercise, subjects ingested capsules containing placebo and 1.5 or 3 mg/kg BW of caffeine using a double-blind administration protocol. Trials consisted of 120 min steady-state cycling at approximately 70% VO2peak, immediately followed by a 7-kJ/kg BW time trial (TT). During exercise, subjects were provided with fluids containing 14C-glucose every 20 min to determine exogenous CHO oxidation. Results: No significant TT performance improvements were observed during caffeine-containing trials (mean ± SD: placebo = 30 min 25 s ± 3 min 10 s; 1.5 mg/kg BW = 30 min 42 s ± 3 min 41 s; and 3 mg/kg BW = 29 min 51 s ± 3 min 38 s). Furthermore, caffeine failed to significantly alter maximal exogenous CHO oxidation (maximal oxidation rates: placebo = 0.95 ± 0.2 g/min; 1.5 mg·kg-1 BW = 0.92 ± 0.2 g/min; and 3 mg/kg BW = 0.96 ± 0.2 g/min). Conclusion: Low and moderate doses of caffeine have failed to improve endurance performance in fed, trained subjects.
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