Previous studies have shown a rapid reduction in postexercise local sweating and blood flow despite elevated core temperatures. However, local heat loss responses do not illustrate how much whole-body heat dissipation is reduced, and core temperature measurements do not accurately represent the magnitude of residual body heat storage. Whole-body evaporative (H˙E) and dry (H˙D) heat loss as well as changes in body heat content (ΔHb) were measured using simultaneous direct whole-body and indirect calorimetry.
Eight participants cycled for 60 min at an external work rate of 70 W followed by 60 min of recovery in a calorimeter at 30°C and 30% relative humidity. Core temperature was measured in the esophagus (T es), rectum (T re), and aural canal (T au). Regional muscle temperature was measured in the vastus lateralis (T vl), triceps brachii (T tb), and upper trapezius (T ut).
After 60 min of exercise, average ΔHb was +273 ± 57 kJ, paralleled by increases in T es, T re, and T au of 0.84 ± 0.49, 0.67 ± 0.36, and 0.83 ± 0.53°C, respectively, and increases in T vl, T tb, and T ut of 2.43 ± 0.60, 2.20 ± 0.64, and 0.80 ± 0.20°C, respectively. After a 10-min recovery, metabolic heat production returned to pre-exercise levels, and H˙E was only 22.9 ± 6.9% of the end-exercise value despite elevations in all core temperatures. After a 60-min recovery, ΔHb was +129 ± 58 kJ paralleled by elevations of T es = 0.19 ± 0.13°C, T re = 0.20 ± 0.03°C, T au = 0.18 ± 0.04°C, T vl = 1.00 ± 0.43°C, T tb = 0.92 ± 0.46°C, and T ut = 0.31 ± 0.27°C. Despite this, H˙E returned to preexercise levels. Only minimal changes in H˙D occurred throughout.
We confirm a rapid reduction in postexercise whole-body heat dissipation by evaporation despite elevated core temperatures. Consequently, only 53% of the heat stored during 60 min of exercise was dissipated after 60 min of recovery, with the majority of residual heat stored in muscle tissue.
1Laboratory of Human Bioenergetics and Environmental Physiology, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, CANADA; 2Yellow Springs, OH; and 3Defence R&D Canada, Quebec City, Quebec, CANADA
Address for correspondence: Glen P. Kenny, Ph.D., School of Human Kinetics, University of Ottawa, 125 University, Montpetit Hall, Ottawa, Ontario, Canada K1N 6N5; E-mail: email@example.com.
Submitted for publication January 2008.
Accepted for publication March 2008.