Abstract
Sweat is a hypotonic fluid excreted by sweat glands to cool the body. There are conflicting reports on whether or not body composition has an effect on thermoregulatory responses especially during exercise. This study was aimed at determining and comparing sweat rate and electrolyte composition in underweight (BMI 2), normal weight (18.5 kg/m2 > BMI 2), overweight (25kg/m2 2) and obese women (BMI > 30 kg/m2) during moderate exercise. Forty women (19 - 25 years) were used during this study after assessing their health status. They were stratified for BMI with each group having a total of ten women. It was ensured that all the women used in the study were euhydrated before commencing the research. Before sweat collection, the treadmill was calibrated according to the Bruce Treadmill Protocol. Sweat samples were obtained with a sweat suction apparatus from a 120 cm2 circular area marked on the skin of the face and neck, after a 15 minute fast walk on a treadmill at an inclination of 15° and at a speed of 4.2 km/h at 27°C room temperature. The time at which sweating commenced in the subjects was recorded. Sweat rate (L/hour) was calculated using the formula: sweat rate (L/hr) = (pre-exercise body weight - Post-exercise body weight)/exercise duration. Each sweat sample was collected and analysed immediately. The results showed that obese women had a significantly (P < 0.05) higher sweat rate and underweight women had a significantly (P < 0.05) lower sweat rate than all the other groups. Furthermore, subjects with a high body surface area showed significantly higher sweat rates compared to subjects with lower body surface area. Sweat electrolyte composition did not change in all BMI groups. In conclusion, obese subjects are more likely to develop fluid imbalances than underweight and normal weight subjects during moderate exercise. Also, underweight women might be at a thermoregulatory disadvantage because of their reduced body fat and body surface area.
Highlights
Sweating is a major form of thermoregulation in man
Thermoregulation is a complex system involving chemical, physical and behavioural events that permit the maintenance of body temperature within a constant range under conditions of variable external or internal heat loads [1]
The results showed that there was no significant change in sweat electrolyte composition in all Body mass index (BMI) groups during the exercise
Summary
Significant amounts of heat is produced by the body and thermoregulatory mechanisms come into play to return body temperature back to the normal range. Notable amongst these mechanisms is sweat production by the sweat glands [2]. The evaporation of sweat from the skin transfers heat to the environment as water has a high latent heat of evaporation. These same mechanisms occur in hot environmental temperature conditions
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