Sweating, thirst perception and plasma electrolyte composition in women of varying body mass indices during moderate exercise

Abstract

Thirst is a perception, the subjective experience evoked by fluid deficits. Exercise induces sweating and subsequently electrolyte loss and thirst but there is little documented on post exercise thirst perception in women of varying body mass indices. 40 apparently healthy young women (19-25years) in the follicular phase of the menstrual cycle were used in this study. On the days scheduled for the experiment, the subjects drank 600 mls of water two hours before exercise to ensure they were euhydrated. The exercise was performed on a treadmill calibrated according to the Bruce treadmill protocol. Immediately after exercise, the subjects were weighed again. Sweat rate (L/hour) was calculated using the formula: Sweat rate (L /hour) = (Pre-exercise body weight ˗ Post-exercise body weight)/exercise duration. Blood samples were collected from the antecubital vein of the subjects into lithium heparin bottles. The samples were immediately centrifuged to obtain the plasma for electrolyte analysis at baseline and post exercise. Thirst perception (TP)(cm) was rated after moderate exercise using a visual analogue scale (VAS). Subjects rated their TP by making a mark across the uncaliberated 10 cm scale, the ends of which were labelled “very thirsty” and “not thirsty”. Results showed a significantly positive (P<0.05) relationship between BMI and sweating. Plasma-chloride levels increased significantly (P<0.05) in overweight and obese subjects, post exercise. Also, there was a significantly (P<0.05) positive relationship between sweat rate and thirst perception after the exercise. In conclusion, thirst perception increases with increasing BMI because of their higher fluid and electrolyte loss during exercise. Overweight, especially obese subjects have an increased risk to develop fluid and chloride imbalances than their lean counterparts during exercise. There might be need for fluid and electrolyte replacement during exercise especially in subjects with higher Body Mass Indices.

Keywords: Sweating, Thirst Perception, Blood electrolyte composition, Body Mass Index, Moderate exercise.