Purpose: This study aimed to investigate whether carbohydrate ingestion during 3 h long endurance exercise in highly trained cyclists at a rate of 120 g h-1 in 0.8:1 ratio between fructose and glucose-based carbohydrates would result in higher exogenous and lower endogenous carbohydrate oxidation rates as compared to ingestion of 90 g h-1 in 1:2 ratio, which is the currently recommended approach for exercise of this duration.
Methods: Eleven male participants (V̇O2peak 62.6 ± 7 mL kg-1 min-1, gas exchange threshold (GET) 270 ± 17 W and Respiratory compensation point 328 ± 32 W) completed the study involving 4 experimental visits consisting of 3 h cycling commencing after an overnight fast at an intensity equivalent to 95% GET. During the trials they received carbohydrates at an average rate of 120 or 90 g h-1 in 0.8:1 or 1:2 fructose-maltodextrin ratio, respectively. Carbohydrates were naturally high or low in 13C stable isotopes enabling subsequent calculations of exogenous and endogenous carbohydrate oxidation rates.
Results: Exogenous carbohydrate oxidation rates were higher in the 120 g h-1 condition (120-180 min: 1.51 ± 0.22 g min-1) as compared to the 90 g h-1 condition (1.29 ± 0.16 g min-1; p = 0.026). Endogenous carbohydrate oxidation rates did not differ between conditions (2.15 ± 0.30 and 2.20 ± 0.33 g min-1 for 120 and 90 g h-1 conditions, respectively; p = 0.786).
Conclusions: The results suggest that carbohydrate ingestion at 120 g h-1 in 0.8:1 fructose-maltodextrin ratio as compared with 90 g h-1 in 1:2 ratio offers higher exogenous carbohydrate oxidation rates but no additional sparing of endogenous carbohydrates. Further studies should investigate potential performance effects of such carbohydrate ingestion strategies.
Keywords: Carbohydrate supplementation; Carbohydrates; Endurance exercise; Exercise metabolism; Exogenous carbohydrate oxidation.
© 2022. The Author(s).