Short-term exercise training does not improve whole-body heat loss when rate of metabolic heat production is considered

Abstract

We evaluated the effects of an 8-week exercise training program in previously sedentary individuals on whole-body heat balance during exercise at a constant rate of metabolic heat production. Prior to and after 8 weeks of training, ten participants performed 60-min of cycling exercise at a constant rate of heat production (approximately 450 W) followed by 60-min of recovery, at 30 degrees C and 15% relative humidity. Rate of total heat loss was measured directly by whole-body calorimetry, while rate of metabolic heat production was measured simultaneously by indirect calorimetry. Esophageal (T(es)), skin blood flow (SkBF) and local sweat rate (LSR) were also measured continuously. The 8-week exercise training program elicited a 10% increase in maximal aerobic capacity (P < 0.001). Furthermore, exercise training reduced (P <or= 0.05) baseline (37.10 +/- 0.28 vs. 36.95 +/- 0.24 degrees C) and end-exercise (37.85 +/- 0.30 vs. 37.55 +/- 0.20 degrees C) values for T (es) as well as onset thresholds for LSR (37.23 +/- 0.26 vs. 36.96 +/- 0.22 degrees C, P < 0.001) and SkBF (37.16 +/- 0.38 vs. 36.83 +/- 0.26 degrees C, P < 0.001). However, these improvements in thermoregulatory function did not translate into a greater rate of total heat loss between the pre- and post-training exercise trials (P = 0.762). Furthermore, there were no differences in SkBF (P = 0.546) and LSR (P = 0.475) from pre- to post-training. Although physical training resulted in significant improvements of cardiorespiratory and thermoregulatory functions, these adaptations did not improve whole-body and local heat loss responses during exercise performed at a given rate of metabolic heat production.