Carbohydrate metabolism during exercise in hot and thermoneutral environments

Area of Science:

• Exercise Physiology
• Environmental Physiology
• Sports Science

Background:

• Understanding fuel utilization during exercise is crucial for optimizing athletic performance.
• Heat stress significantly impacts physiological responses during physical exertion.
• Limited data exists on carbohydrate metabolism during exercise in heat for acclimatized athletes.

Purpose of the Study:

• To compare the effects of moderately intense exercise in hot versus thermoneutral environments on muscle glycogen and carbohydrate utilization.
• To investigate physiological differences in well-trained, heat-acclimatized cyclists under varying thermal conditions.

Main Methods:

• Seven heat-acclimatized cyclists performed a 60-minute cycling bout at 73.6% maximal oxygen consumption.
• Exercise was conducted in both a thermoneutral (23.5°C) and a hot (33.7°C) environment.
• Muscle biopsies, physiological measurements (rectal temperature, heart rate), and blood markers were analyzed pre- and post-exercise.

Main Results:

• Exercise in heat elevated rectal temperature and heart rate, while reducing body weight and plasma volume compared to thermoneutral conditions.
• Plasma glucose and blood lactate increased more significantly during exercise in the heat.
• Crucially, no differences were observed in carbohydrate oxidation or muscle glycogen utilization between the hot and thermoneutral environments.

Conclusions:

• Moderately intense exercise in hot environments does not accelerate muscle glycogenolysis or carbohydrate oxidation in well-conditioned, heat-acclimatized individuals.
• Despite altered physiological responses, substrate utilization for carbohydrate remains consistent under these specific exercise conditions.
• Heat acclimatization appears to mitigate the impact of heat on carbohydrate metabolism during sustained exercise.