Little is known about energy yield during exercise in the heat in boys compared to men. To investigate substrate utilization with and without exogenous carbohydrate (CHOexo) intake, seven boys (11.2 ± 0.5 yrs) and nine men (24.0 ± 3.3 yrs) cycled (4×20 min bouts) at a fixed metabolic heat production (H.p) per unit body mass (6 W×kg-1) in a climate chamber (38°C and 50% relative humidity), on two occasions. Participants consumed a 13C-enriched 8% CHO beverage (CARB) or placebo beverage (CONT) in a double-blinded, counter balanced manner. Substrate utilization was calculated for the last 60 min of exercise. CHOexo oxidation rate (2.0 ± 0.3 vs. 2.5 ± 0.2 mg×kgFFM-1×min-1, P = 0.02) and CHOexo oxidation efficiency (12.8 ± 0.6 vs. 16.0 ± 0.9 %, P = 0.01) were lower in boys compared to men exercising in the heat. Total carbohydrate (CHOtotal), endogenous CHO (CHOendo) and total fat (FATtotal) remained stable in boys and men (P > 0.05) during CARB, whereas CHOtotal oxidation rate decreased (P < 0.001) and FATtotal oxidation rate increased over time similarly in boys and men during CONT (P < 0.001). The relative contribution of CHOexo to total energy yield increased over time in both groups (P < 0.001). In conclusion, endogenous substrate metabolism and the relative contribution of fuels to total energy yield were not different between groups. The ingestion of a CHO beverage during exercise in the heat may be as beneficial for boys and men to spare endogenous substrate.
- substrate utilization
- Copyright © 2016, Journal of Applied Physiology