Substrate utilization in boys during exercise with [13C]-glucose ingestion.

Area of Science:

• Exercise Physiology
• Nutritional Biochemistry
• Sports Science

Background:

• Substrate utilization during prolonged exercise in adolescents is not well understood.
• Exogenous glucose (GLUexo) ingestion's impact on this process remains unknown.

Purpose of the Study:

• To determine the effect of intermittent GLUexo ingestion on substrate utilization during prolonged exercise in adolescent boys (ages 13-17).

Main Methods:

• Adolescent boys completed four 30-min exercise bouts at 60% max O2 consumption, with intermittent water (control trial, CT) or 13C-enriched GLUexo (glucose trial, GT) ingestion.
• Substrate oxidation (carbohydrates, fats) was measured via indirect calorimetry.
• GLUexo oxidation was determined using 13C/12C ratios in expired air.
• Hormonal and metabolic markers (insulin, glucose, free fatty acids, glycerol) and perceived exertion (RPE) were monitored.

Main Results:

• Total carbohydrate oxidation increased by 20% in GT compared to CT (P < 0.01), while total fat oxidation decreased by 45% (P < 0.01).
• GLUexo contributed 57.8 g (34.2%) to total oxidation in GT.
• Endogenous glucose oxidation was reduced by 14% in GT (P < 0.01).
• Insulin and glucose levels were higher, while free fatty acids and glycerol were lower in GT (P < 0.05).
• RPE was significantly lower in GT compared to CT.

Conclusions:

• Intermittent GLUexo intake during prolonged exercise spares endogenous carbohydrate and fat oxidation in adolescent boys.
• GLUexo contributes significantly to energy provision and reduces the perception of effort during exercise.
• These findings have implications for nutritional strategies in young athletes.