Effects Of Drink Temperature After Exercise: Thermoregulatory Responses And Accuracy Of Ingestible Temperature Capsules

Abstract

There is no data available for the thermoregulatory responses to ingesting drinks of different temperatures after exercise. PURPOSE: To investigate the effects of ingestion of drinks at 4°C or 28°C after exercise on the thermoregulatory responses to subsequent work in the heat. The accuracy of core temperature, measured via ingestible temperature capsules, after ingesting drinks of different temperatures was also validated. METHODS: Eight healthy males walked on the treadmill for two cycles at 5.5 km/h with 7.5% gradient for 45 min with 15 min of seated rest in a warm and humid environment (dry bulb temperature of 32°C with 65% humidity). An ingestible temperature capsule was ingested 8-11 h prior to all experimental trials for measurement of gastrointestinal temperature (Tint). During each 15 min rest period, a total of 800 ml of plain water at 4°C or 28°C was consumed at the 3rd and 8th min. Drinks at 38°C were ingested during a familiarization trial prior to the two experimental trials. Rectal temperature (Tre), skin temperatures (Tsk), heart rate and rating of thermal sensation were measured. RESULTS: Mean decrease in Tre at the end of both cycles was greater after the ingestion of drinks at 4°C (0.5 ± 0.2°C; Mean±SD) than drinks at 28°C (0.3 ± 0.2°C; P < 0.05). Coefficient of determination (R2) between Tre and Tint decreased following the ingestion of drinks (4°C: R2 = 0.89 to 0.11; 28°C: R2 = 0.78 to 0.63; P < 0.001). Decrease in Tsk was greater during the 1st bout of rest after ingestion of drinks at 4°C (0.7 ± 0.3°C) relative to ingestion of drinks at 28°C (0.5 ± 0.3°C; P < 0.01). Mean heart rate was lower after ingesting drinks at 4°C (115 ± 13 bpm) than at 28°C (122 ± 12 bpm; P < 0.05) until the 20th min of the 2nd bout of work cycle. As compared to ingestion of drinks at 28°C (1 ± 1; 'Slightly Warm'), rating of thermal sensation was lower during the 2nd bout of rest after ingestion of drinks at 4°C (0 ± 1; 'Neutral'; P < 0.05). CONCLUSIONS: As compared with drinks at 28°C, ingestion of drinks at 4°C after exercise resulted in a greater decrease in body core temperature with minimum thermal discomfort, implying a possible potential for improved work tolerance in the heat. The accuracy of Tint was decreased after ingestion of drinks at temperatures lower than normal body core temperature with a greater effect with drinks at 4°C than with drinks at 28°C.