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.