Submitted on October 4, 2007
Accepted on March 10, 2008
Human heat balance during postexercise recovery: separating metabolic and nonthermal effects
Ollie Jay1, Daniel Gagnon1, Michel B. DuCharme2, Paul Webb3, Francis D Reardon1, and Glen P. Kenny1*
1 School of Human Kinetics, University of Ottawa, Ottawa, Canada
2 Defence R&D Canada, Quebec City, Canada; School of Human Kinetics, University of Ottawa, Ottawa, Canada
3 Yellow Springs, Ohio, United States
* To whom correspondence should be addressed. E-mail: gkenny{at}uottawa.ca.
Previous studies report greater postexercise heat loss responses during active recovery relative to inactive recovery despite similar core temperatures between conditions. Differences have been ascribed to nonthermal factors influencing heat loss response control since elevations in metabolism during active recovery are assumed to be insufficient to change core temperature and modify heat loss responses. However, from a heat balance perspective, different rates of total heat loss with corresponding rates of metabolism are possible at any core temperature. Seven male volunteers cycled at 75% of VO2peak in the Snellen whole-body air calorimeter regulated at 25.0°C, 30% RH, for 15-min followed by 30-min of active (AR) or inactive (IR) recovery. Relative to IR, a greater rate of metabolic heat production (M-W) during AR was paralleled by a greater rate of total heat loss (HL) and a greater local sweat rate, despite similar esophageal temperatures between conditions. At end-recovery, rate of body heat storage (i.e.[(M-W)-HL] approached zero similarly in both conditions, with M-W and HL elevated during AR by 91±26 W and 93±25 W respectively. Despite a higher M-W during AR, change in body heat content from calorimetry was similar between conditions due to a slower relative decrease in HL during AR, suggesting an influence of nonthermal factors. In conclusion, different levels of heat loss are possible at similar core temperatures during recovery modes of different metabolic rates. Evidence for nonthermal influences upon heat loss responses must therefore be sought after accounting for differences in heat production.
