Current recommendations for CHO intake in the field for all modes of endurance exercise are largely on the basis of laboratory studies that measured oxidation of ingested CHO. However, the majority of these laboratory studies used cycling as the mode of exercise, and it is not known whether these results can be extrapolated to running.
Purpose: the purpose of this study was to investigate exogenous CHO oxidation from a CHO drink during moderate-intensity running (RUN) compared with cycling (CYCLE).
Methods: eight athletes with comparable CYCLE and RUN training backgrounds (mean ± SD: age = 37 ± 7 yr, weight = 75 ± 7 kg, height = 1.77 ± 0.05 m; V˙O2max CYCLE = 63 ± 3 mL·kg·min, V˙O2max RUN = 65 ± 4 mL·kg·min) performed four exercise trials in random order. The trials consisted of either running or cycling at approximately 60% of the exercise specific V˙O2max for 120 min while receiving either a CHO drink (2:1 glucose-fructose blend; 1.5 g·min) or a similar volume of plain water (WAT; 675 mL·h).
Results: the set workload elicited similar relative exercise intensities of 59.7% ± 2.0% and 59.2% ± 1.9% V˙O2max for RUN and CYCLE, respectively. Peak and average exogenous CHO oxidation rates were not significantly different between RUN and CYCLE trials and showed a similar time course (peak at 120 min = 1.25 ± 0.10 vs 1.19 ± 0.08 g·min, respectively, P = 0.13; average over final hour = 1.14 ± 0.10 and 1.11 ± 0.11 g·min, respectively, P = 0.94). Furthermore, total fat oxidation rates were higher during RUN compared with CYCLE. The difference was significant with ingestion of WAT (P = 0.02) and failed to reach statistical significance with CHO (P = 0.09).
Conclusions: this study demonstrates that exogenous CHO oxidation rates are similar between prolonged running and cycling at a similar relative moderate intensity. These data suggest that previous exogenous CHO oxidation results from cycling studies can be extrapolated to running.