Abstract
Background: Hypohydration is a common occurrence across many different sporting codes and has been shown to impair exercise performance through increased cardiovascular strain. Previous studies have induced hypohydration in participants by 2-5% body mass and reported subsequent exercise to result in increased heart rate (HR) and core temperature, along with reduced sweat rate and decreased performance. However, little is known about the effect mild levels of hypohydration has on the physiological and psychological factors of HR, sweat rate and rate of perceived exertion (RPE). There is even less research carried out on females, which is why they were chosen as the participants for this study.
Objective: To investigate whether mild levels of habitual hypohydration before exercise affect HR, RPE or sweat rate.
Methods: This was a cross sectional study with 14 healthy, recreationally active, female participants. Participants completed two identical exercise trials separated by at least a week. They arrived at the clinic in the morning after an overnight fast and completed a subjective questionnaire relating to feelings of thirst, which was repeated after exercise. Participants then cycled for 60 minutes, which comprised of four 10 minute bouts at 2watts/kg followed by 5 minutes of rest. HR and RPE were taken at 15 minute intervals during exercise. The exercise environment was kept at an average of 87% humidity and 21oC to induce sweating. Sweat loss was calculated via weighing the participants before and after exercise. Urine samples were collected pre and post exercise along with a 24-hour urine collection on the day prior to the exercise trials; these were all analysed for osmolality and urine specific gravity (USG).
Results: Pre exercise urine osmolality was not associated with HR, RPE or sweat rate during exercise. Sweat loss during exercise was associated with mean RPE (p=0.036), with 1kg weight loss during exercise associated with a 0.7 increase in RPE. Pre exercise urine osmolality and USG were highly correlated (r=0.96).
Conclusion: The main finding of the study was that a small change in body mass (<1% body weight) during exercise was associated with an increase in average RPE. This adds to the current research as it shows that a slight decrease in total body water can evoke a psychological effect in exercising females. This may have implications when recommending fluid intakes for females engaging in exercise.