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 (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.
Human and Environmental Physiology Research Unit, Laboratory of Human Bioenergetics and Environmental Physiology, Faculty of Health Sciences, School of Human Kinetics, University of Ottawa, 125 University, Montpetit Hall, Room 367, Ottawa, ON, Canada.
Jill
J
Stapleton
Daniel
D
Gagnon
Glen P
GP
Kenny
D000222:Adaptation, Physiological; D000293:Adolescent; D001642:Bicycling; D001794:Blood Pressure; D001823:Body Composition; D001833:Body Temperature Regulation; D002153:Calorimetry, Indirect; D004734:Energy Metabolism; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008954:Models, Biological; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000378:metabolism*; D005082:Physical Exertion; D010809:Physical Fitness; D012039:Regional Blood Flow; D057185:Sedentary Behavior; D012867:Skin / Q000098:blood supply*; D012881:Skin Temperature; D013546:Sweating; D013997:Time Factors; D055815:Young Adult