Riddell, M. C., Timmons, B. W., & Bar-Or, O. (2002). Substrate utilization with and without 13C-enriched carbohydrate intake in boys and men. Medicine and Science in Sports and Exercise, 34(5), Supplement abstract 1146.

This study compared substrate utilization between boys and men during exercise performed with and without 13C-enriched exogenous carbohydrate (13CHO) intake. Boys (N = 12) and men (N = 10) cycled for 60 minutes at 70% VO2max on two occasions. A placebo or CHO (6% glucose-electrolyte beverage) was consumed.

Respiratory exchange ratio (RER) decreased throughout the performance in both groups but was significantly lower for boys than men. With CHO intake, RER decreased for men but remained relatively constant for boys. The percent contribution of CHO (exogenous) to total energy yield during the final 30 minutes of exercise was significantly higher in boys (~24%) than men (~14%).

Implication. Without CHO intake, pre and early pubertal boys rely more on fat and less on endogenous CHO compared to men during exercise performed at the same relative intensity. With exogenous CHO, the relative energy contribution from CHO oxidation is higher, and the endogenous CHO sparing greater in boys than men. Thus, CHO intake might be particularly beneficial for younger boys than men.

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