Independent and combined effects of carbohydrate and caffeine ingestion on aerobic cycling performance in the fed state

The purpose of this study was to examine the independent and combined effects of carbohydrate and caffeine ingestion on performance and various physiological parameters during aerobic cycling (similar to 1 h). Ten male cyclists (28 +/- 9 years, 73 +/- 6 kg, 66 +/- 9 mL.kg(-1).min(-1) maximal oxygen consumption) performed 20 min of steady-state (SS) cycling (60% peak power (W-max)) followed by a simulated 20-km time trial (TT) under placebo (PLA), carbohydrate (CHO), caffeine (CAF), and combined CAF-CHO conditions, all of which were performed in the fed state. CAF-CHO improved TT performance by 3.4% +/- 2% (84 +/- 57 s) compared with PLA (p < 0.05), whereas no differences were detected among CHO, CAF, and PLA. The SS respiratory exchange ratio was elevated in CHO (0.92 +/- 0.03), CAF (0.96 +/- 0.07), and CAF-CHO (0.95 +/- 0.02) compared with PLA (0.89 +/- 0.03) (p < 0.05). Post-SS and post-TT blood glucose levels were also elevated in CAF-CHO (88.3 +/- 16.7 mg.dL(-1) and 111.2 +/- 33.5 mg.dL(-1), respectively) compared with PLA (74.5 +/- 9.8 mg.dL(-1) and 85.4 +/- 17.6 mg.dL(-1), respectively) (p < 0.05). Treatment conditions did not differentially impact SS pulmonary ventilation, oxygen consumption, heart rate, peak quadriceps muscle strength, rating of perceived exertion, or blood lactate. CAF and CHO improved TT performance when taken together but not independently. Although the present work did not yield any definitive physiological mechanisms for the performance findings, these data suggest that cyclists in the fed state should ingest carbohydrate and caffeine together to improve time trial performance.