The objective of this study was to examine the effect of ingested water temperature on heat balance during exercise as assessed by direct calorimetry.
Ten healthy males (25 ± 4 yr) cycled at 50% V˙O2peak (equivalent rate of metabolic heat production (M-W) of 523 ± 84 W) for 75 min under thermocomfortable conditions (25°C, 25% relative humidity) while consuming either hot (50°C) or cold (1.5°C) water. Four 3.2 mL·kg−1 boluses of hot or cold water were consumed 5 min before and at 15, 30, and 45 min after the onset of exercise. Total heat loss (H L = evaporative heat loss (H E) ± dry heat exchange (H D)) and M-W were measured by direct and indirect calorimetry, respectively. Change in body heat content (ΔH b) was calculated as the temporal summation of M-W and H L and adjusted for changes in heat transfer from the ingested fluid (H fluid).
The absolute difference for H L (209 ± 81 kJ) was similar to the absolute difference of H fluid (204 ± 36 kJ) between conditions (P = 0.785). Furthermore, the difference in H L was primarily explained by the corresponding changes in H E (hot: 1538 ± 393 kJ; cold: 1358 ± 330 kJ) because H D was found to be similar between conditions (P = 0.220). Consequently, no difference in ΔH b was observed between the hot (364 ± 152 kJ) and cold (363 ± 134 kJ) conditions (P = 0.971) during exercise.
We show that ingestion of hot water elicits a greater H L relative to cold water ingestion during exercise. However, this response was only compensated for the heat of the ingested fluid as evidenced by similar ΔH b between conditions. Therefore, our findings indicate that relative to cold water ingestion, consuming hot water does not provide a thermoregulatory advantage. Both hot and cold water ingestion results in the same amount of heat stored during prolonged moderate-intensity exercise.
Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, CANADA
Address for correspondence: Glen P. Kenny, Ph.D., Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, 125 University Private, Room 367, Montpetit Hall, Ottawa, Ontario, Canada K1N 6N5; E-mail: email@example.com.
Submitted for publication July 2014.
Accepted for publication September 2014.