Body heat storage during physical activity is lower with hot fluid ingestion under conditions that permit full evaporation

Acta Physiol (Oxf). 2012 Oct;206(2):98-108. doi: 10.1111/j.1748-1716.2012.02452.x. Epub 2012 Jun 9.


Aim: To assess whether, under conditions permitting full evaporation, body heat storage during physical activity measured by partitional calorimetry would be lower with warm relative to cold fluid ingestion because of a disproportionate increase in evaporative heat loss potential relative to internal heat transfer with the ingested fluid.

Methods: Nine males cycled at 50% VO(2max) for 75 min at 23.6 ± 0.6 °C and 23 ± 11% RH while consuming water of either 1.5 °C, 10 °C, 37 °C or 50 °C in four 3.2 mL kg(-1) boluses. The water was administered 5 min before and 15, 30 and 45 min following the onset of exercise.

Results: No differences in metabolic heat production, sensible or respiratory heat losses (all P > 0.05) were observed between fluid temperatures. However, while the increased internal heat loss with cold fluid ingestion was paralleled by similar reductions in evaporative heat loss potential at the skin (E(sk) ) with 10 °C (P = 0.08) and 1.5 °C (P = 0.55) fluid, the increased heat load with warm (50 °C) fluid ingestion was accompanied by a significantly greater E(sk) (P = 0.04). The resultant calorimetric heat storage was lower with 50 °C water ingestion in comparison to 1.5 °C, 10 °C and 37 °C (all P < 0.05). In contrast, heat storage derived conventionally using thermometry yielded higher values following 50 °C fluid ingestion compared to 1.5 °C (P = 0.025).

Conclusion: Under conditions permitting full sweat evaporation, body heat storage is lower with warm water ingestion, likely because of disproportionate modulations in sweat output arising from warm-sensitive thermosensors in the esophagus/stomach. Local temperature changes of the rectum following fluid ingestion exacerbate the previously identified error of thermometric heat storage estimations.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Analysis of Variance
  • Bicycling*
  • Body Temperature Regulation*
  • Calorimetry
  • Cold Temperature
  • Drinking*
  • Exercise*
  • Heart Rate
  • Hot Temperature*
  • Humans
  • Male
  • Models, Biological
  • Oxygen Consumption
  • Skin Temperature
  • Sweating*
  • Thermogenesis
  • Time Factors
  • Young Adult