Sweating rate and sweat composition during exercise and recovery in ambient heat and humidity

Abstract

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.

Super‐Absorbent Polymer Valves and Colorimetric Chemistries for Time‐Sequenced Discrete Sampling and Chloride Analysis of Sweat via Skin‐Mounted Soft Microfluidics

“…Traditional methods use cotton sponges and gauze to capture sweat for follow‐on laboratory analysis. These methods are laborious, require specialized training, and introduce risks of evaporation and contamination with exposure to the atmosphere . Although recent advances have demonstrated the feasibility of collecting and analyzing sweat in real time, numerous technical challenges still remain .…”

“…First, information should be provided simply, directly, and immediately to the user while minimizing the necessary steps to infer data with electronic readers or mobile phones . Second, the device must isolate sufficient volumes for multiple assay samples without crosscontamination or evaporation . Finally, the operation should afford capabilities in continuous monitoring but without prolonged contact of sweat with the skin itself to minimize skin irritation.…”

Fluid and electrolyte supplementation after prolonged moderate-intensity exercise enhances muscle glycogen resynthesis in Standardbred horses

“…Therefore, it is reasonable to postulate that postexercise dehydration affected muscle glycogen replenishment in the present study. In contrast to humans, equine sweat is hypertonic to plasma (44), resulting in an exercise-induced plasma dehydration that is isotonic to hypotonic. Thus, when electrolytes lost in sweat are not replaced, there is no increase in plasma osmolality to stimulate a thirst response.…”

Potassium-free electrolytes and calcium supplementation in an endurance race

“…The intake of electrolytes was recorded during the race. The formula of EM 2 K was based on estimated sweat composition 19,20 , except that K was not included, and each dose was formulated to provide the amount of sodium, calcium, magnesium, chloride and phosphate lost in 2.5 l of sweat 7 . Each dose consisted of 21.8 g of sodium chloride, 1.7 g of calcium chloride, 1.1 g of magnesium chloride and 0.13 g of monosodium monophosphate.…”