The effects of acute carbohydrate and caffeine feeding strategies on cycling efficiency

To assess the effect of carbohydrate and caffeine on gross efficiency (GE), 14 cyclists (V̇O_2max 57.6 ± 6.3 ml.kg^-1.min^-1) completed 4 × 2-hour tests at a submaximal exercise intensity (60% Maximal Minute Power). Using a randomized, counter-balanced crossover design, participants consumed a standardised diet in the 3-days preceding each test and subsequently ingested either caffeine (CAF), carbohydrate (CHO), caffeine+carbohydrate (CAF+CHO) or water (W) during exercise whilst GE and plasma glucose were assessed at regular intervals (~30 mins). GE progressively decreased in the W condition but, whilst caffeine had no effect, this was significantly attenuated in both trials that involved carbohydrate feedings (W = -1.78 ± 0.31%; CHO = -0.70 ± 0.25%, p = 0.008; CAF+CHO = -0.63 ± 0.27%, p = 0.023; CAF = -1.12 ± 0.24%, p = 0.077). Blood glucose levels were significantly higher in carbohydrate ingestion conditions (CHO = 4.79 ± 0.67 mmol·L^-1, p < 0.001; CAF+CHO = 5.05 ± 0.81 mmol·L^-1, p < 0.001; CAF = 4.46 ± 0.75 mmol·L^-1; W = 4.20 ± 0.53 mmol·L^-1). Carbohydrate ingestion has a small but significant effect on exercise-induced reductions in GE, indicating that cyclists' feeding strategy should be carefully monitored prior to and during assessment.