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

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 (similar to 450 W) followed by 60-min of recovery, at 30A 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 a parts per thousand currency sign 0.05) baseline (37.10 +/- A 0.28 vs. 36.95 +/- A 0.24A degrees C) and end-exercise (37.85 +/- A 0.30 vs. 37.55 +/- A 0.20A degrees C) values for T (es) as well as onset thresholds for LSR (37.23 +/- A 0.26 vs. 36.96 +/- A 0.22A degrees C, P < 0.001) and SkBF (37.16 +/- A 0.38 vs. 36.83 +/- A 0.26A 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.