Temperature of Ingested Water during Exercise Does Not Affect Body Heat Storage.

Area of Science:

• Exercise Physiology
• Thermoregulation
• Human Heat Balance

Background:

• Understanding how ingested fluid temperature affects thermoregulation during exercise is crucial for optimizing athletic performance and safety.
• Previous research has yielded mixed results regarding the impact of water temperature on physiological responses during physical activity.

Purpose of the Study:

• To investigate the influence of ingested hot versus cold water on the body's heat balance during moderate-intensity cycling exercise.
• To determine if consuming hot water offers a thermoregulatory advantage compared to cold water during prolonged exercise.

Main Methods:

• Ten healthy males performed 75-minute cycling sessions at 50% peak oxygen uptake under controlled environmental conditions.
• Participants ingested either hot (50°C) or cold (1.5°C) water in boluses before and during exercise.
• Direct and indirect calorimetry were used to measure total heat loss, metabolic heat production, and changes in body heat content, accounting for heat transfer from ingested fluids.

Main Results:

• Total heat loss was greater following hot water ingestion compared to cold water, primarily due to increased evaporative heat loss.
• Dry heat exchange did not differ significantly between the hot and cold water conditions.
• Despite differences in total heat loss, the change in body heat content remained similar between the hot and cold water ingestion conditions.

Conclusions:

• Ingesting hot water during exercise increases total heat loss, but this effect is counterbalanced by the heat absorbed from the ingested fluid.
• Consuming hot water does not provide a significant thermoregulatory advantage over cold water during prolonged moderate-intensity exercise.
• Both hot and cold water ingestion result in comparable amounts of heat stored in the body during the studied exercise protocol.