Summary The objective of this study was to determine the composition and extent of sweat losses during submaximal exercise under hot and humid conditions and to compare these findings with the same exercise protocol conducted under cool, dry and hot, dry conditions. Five Thoroughbred horses (age 3 to 6) completed exercise tests under each of 3 environmental conditions in random order: cool, dry (CD), room temperature (T) = 20°C, relative humidity (RH) = 45–55%; hot, dry (HD), T=32–34°C, RH=45–55%; and hot, humid (HH), T=32–34°C, RH=80–85%. Horses exercised at 50% of their predetermined V̇O2max on a treadmill set at a 10% slope until attainment of a pulmonary artery blood temperature of 41.5°C followed by a 60 min recovery. Sweat was collected from a sealed polyethylene pouch enclosing a 150 cm2 area on the lateral thorax. During exercise and the first 30 min of recovery, sweat fluid losses were 7.9 ± 0.7 litres, 9.9 ± 0.5 litres and 6.6 ± 1.2 litres (mean ± s.e.m.) for CD, HD and HH, respectively. Sweating rate (SR), calculated from sweat volume per unit area of enclosed skin, was lowest in CD and similar in HD and HH during exercise such that at end of exercise in HH (16.5 min) calculated sweat losses were approximately 5% and 32% higher than in HD and CD, respectively. In recovery, SR declined in all conditions but was significantly lower in CD (P<0.05). Sweating was detectable until 30 min recovery in CD, 45 min recovery in HD and 60 min recovery in HH. Sweat composition and osmolality was different under the 3 environmental conditions and changed gradually during exercise and recovery in all conditions. Osmolality and [Na] was highest in HD and lowest in CD. During exercise, [Na] increased with increasing SR. Although exercise duration was significantly decreased in HH (16.5 ± 1 min) when compared to HD (28 ± 2 min) and CD (37 ± 2 min), fluid and ion losses in HH were comparable to those in HD as a result of a high SR and prolonged sweating during recovery.
SummaryThe objectives of this study were to compare sweat collection techniques and determine effect of low and high intensity exercise on the composition and osmolality of equine sweat in exercise trained Thoroughbred horses. Sweat collection sites included the neck and thorax, bilaterally and behind the girth ventrally. Sweat was collected in cotton gauze, either exposed to the air or contained within a plastic pouch, from sealed pouches, with or without application of vaseline to the skin, and as it dripped off the skin behind the girth (free catch). There were differences in the ionic composition of sweat collected by different techniques during and after low (50% OOzmax) and after high (90% OOZ,,,~~) intensity exercise. These changes were most consistent where collection technique minimised evaporative losses. With regard to collection method, ionic concentrations and osmolality were lowest in samples obtained from sealed pouches without vaseline on the skin. In samples obtained from cotton gauze and by free catch, osmolality, [Na] and [Cl] were significantly increased when compared with sweat collected from sealed pouches. In samples collected from sealed pouches during low intensity exercise, osmolality increased 11 %, [Na] and [Cl] increased 26% and 9%, respectively and [K] decreased 14%. Osmolality and the concentrations of these ions did not change during recovery. In contrast, osmolality increased by 12% in the first 5 min following high intensity exercise. After both intensities of exercise, there was a significant decrease in the concentration of protein in sweat collected by all methods. Results indicate that collection technique had a marked effect on composition of sweat as demonstrated by increased osmolality and increased concentrations of Na and CI in sweat collected in cotton gauze and by free catch.
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