Energy substrate utilization with and without exogenous carbohydrate intake in boys and men exercising in the heat.
Little is known about energy yield during exercise in the heat in boys compared with men. To investigate substrate utilization with and without exogenous carbohydrate (CHOexo) intake, seven boys [11.2 ± 0.2 (SE) yr] and nine men (24.0 ± 1.1 yr) cycled (4 × 20-min bouts) at a fixed metabolic heat production (Ḣp) per unit body mass (6 W/kg) in a climate chamber (38°C and 50% relative humidity), on two occasions. Participants consumed a13C-enriched 8% CHO beverage (CARB) or placebo beverage (CONT) in a double-blinded, counterbalanced manner. Substrate utilization was calculated for the last 60 min of exercise. CHOexooxidation rate (2.0 ± 0.3 vs. 2.5 ± 0.2 mg·kg fat-free mass-1·min-1, P = 0.02) and CHOexooxidation efficiency (12.8 ± 0.6 vs. 16.0 ± 0.9%, P = 0.01) were lower in boys compared with 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 CHOtotaloxidation rate decreased (P < 0.001) and Fattotaloxidation rate increased over time similarly in boys and men during CONT (P < 0.001). The relative contribution of CHOexoto 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 as men to spare endogenous substrate.
Child Health & Exercise Medicine Program, Department of Pediatrics, McMaster University, Hamilton, Ontario, Canada; and.
Gabriela T
GT
Leites
Child Health & Exercise Medicine Program, Department of Pediatrics, McMaster University, Hamilton, Ontario, Canada; and.|Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
Giovani S
GS
Cunha
Child Health & Exercise Medicine Program, Department of Pediatrics, McMaster University, Hamilton, Ontario, Canada; and.
Lisa
L
Chu
Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
Flavia
F
Meyer
Child Health & Exercise Medicine Program, Department of Pediatrics, McMaster University, Hamilton, Ontario, Canada; and timmonbw@mcmaster.ca.
Brian W
BW
Timmons
D000328:Adult; D000818:Animals; D002648:Child; D004040:Dietary Carbohydrates / Q000378:metabolism*; D004311:Double-Blind Method; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006358:Hot Temperature; D006801:Humans; D050356:Lipid Metabolism / Q000502:physiology; D008297:Male; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000502:physiology; D055815:Young Adult
D004040:Dietary Carbohydrates
children; exercise; heat; hydration; stable isotope; substrate utilization