The dynamics of heat exchange during exercise

Abstract

Purpose. The primary aim of this thesis was to examine the changes in body heat content (DeltaHb) during exercise. Specifically, Study #1 compared DeltaHb and changes in mean body temperature (DeltaT¯b) and DeltaHb from thermometry with direct calorimetry. Study #2 sought to examine the effect of DeltaH b on different time-responses of measures of body temperature. Methods. Study #1 - Forty-one subjects (23 females) performed 60--90 min of cycling exercise at 40% V˙O2peak. DeltaHb, core, muscle and skin temperatures were measured by direct calorimetry, and DeltaH b was also estimated from conventional thermometry equations. Study #2 - Sixteen subjects (8 females) performed 60 min of cycling exercise at 70 W. Changes in DeltaHb as a function of heat gain and heat loss, core and skin temperatures were measured. Results. Study #1 - Measurements of DeltaHb and DeltaT¯b by direct calorimetry were significantly greater than by conventional thermometry (p < 0.01). Study #2 - Esophageal and tympanic temperatures and whole-body heat loss achieved steady values at a significantly earlier time than rectal temperature (p < 0.01). Conclusions. Study #1 - The calculation of DeltaHb by thermometry underestimates body heat content when compared to direct calorimetry, and estimates of DeltaHb by thermometry, must be revised to a three compartment model that includes muscle temperature. Study #2 - As rectal temperature achieved steady state later than all other measures of temperature and heat flow, it best indicates when whole-body thermal steady-state has been reached.