Influence of training on sweating responses during submaximal exercise in horses.
Sweating responses were examined in five horses during a standardized exercise test (SET) in hot conditions (32-34 degrees C, 45-55% relative humidity) during 8 wk of exercise training (5 days/wk) in moderate conditions (19-21 degrees C, 45-55% relative humidity). SETs consisting of 7 km at 50% maximal O(2) consumption, determined 1 wk before training day (TD) 0, were completed on a treadmill set at a 6 degrees incline on TD0, 14, 28, 42, and 56. Mean maximal O(2) consumption, measured 2 days before each SET, increased 19% [TD0 to 42: 135 +/- 5 (SE) to 161 +/- 4 ml. kg(-1). min(-1)]. Peak sweating rate (SR) during exercise increased on TD14, 28, 42, and 56 compared with TD0, whereas SRs and sweat losses in recovery decreased by TD28. By TD56, end-exercise rectal and pulmonary artery temperature decreased by 0.9 +/- 0.1 and 1.2 +/- 0.1 degrees C, respectively, and mean change in body mass during the SET decreased by 23% (TD0: 10.1 +/- 0.9; TD56: 7.7 +/- 0.3 kg). Sweat Na(+) concentration during exercise decreased, whereas sweat K(+) concentration increased, and values for Cl(-) concentration in sweat were unchanged. Moderate-intensity training in cool conditions resulted in a 1.6-fold increase in sweating sensitivity evident by 4 wk and a 0.7 +/- 0.1 degrees C decrease in sweating threshold after 8 wk during exercise in hot, dry conditions. Altered sweating responses contributed to improved heat dissipation during exercise and a lower end-exercise core temperature. Despite higher SRs for a given core temperature during exercise, decreases in recovery SRs result in an overall reduction in sweat fluid losses but no change in total sweat ion losses after training.
McCutcheon
L J
LJ
Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada N1G 2W1. jmccutch@uoguelph.ca
Geor
R J
RJ
D000818:Animals; D001826:Body Fluids / Q000378:metabolism; D001831:Body Temperature; D001835:Body Weight; D004777:Environment; D005260:Female; D006736:Horses / Q000502:physiology*; D007477:Ions; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D010101:Oxygen Consumption; D010805:Physical Conditioning, Animal / Q000502:physiology*; D013542:Sweat / Q000737:chemistry; D013546:Sweating / Q000502:physiology*; D013997:Time Factors
D007477:Ions