Self-selected fluid volume and flavor strength does not alter fluid intake, body mass loss, or physiological strain during moderate-intensity exercise in the heat

Abstract

The purpose of this study was to determine the effects of ad libitum flavor and fluid intake on changes in body mass (BM) and physiological strain during moderate intensity exercise in the heat. Ten subjects (24±3yrs, 7M/3F) performed 60min of treadmill walking at 1.3m/s and 7% grade in an environmental chamber set to 33°C and 10% relative humidity while carrying a 22.7kg pack on two different occasions. Subjects consumed either plain water or water plus flavor (Infuze), ad libitum, at each visit. Pre and post exercise, fluid consumption (change in fluid reservoir weight) and BM (nude) were measured. During exercise, heart rate (HR), systolic blood pressure (SBP), rate of perceived exertion (RPE), oxygen consumption (VO2), respiratory exchange ratio (RER), core temperature (TC), and physiological strain index (PSI) were recorded every 15min during exercise. No significant differences were observed for fluid consumption between fluid conditions (512±97.2mL water vs. 414.3±62.5mL Infuze). Despite a significant decrease from baseline, there were no significant differences in overall change of BM (Δ -1.18 vs. -0.64Kg) or percent body weight loss for water and Infuze conditions, respectively (1.58±0.6 and 0.79±0.2%). Furthermore, there were no significant differences in HR (144±6 vs. 143±8 bpm), SBP (157±5 vs. 155±5mmHg), RPE, VO2 (27.4±0.9 vs. 28.1±1.2ml/Kg/min), RER, TC (38.1±0.1 vs. 37.0±0.1°C), and peak PSI (5.4±0.4 vs. 5.7±0.8) between conditions. Offering individuals the choice to actively manipulate flavor strength did not significantly influence ad libitum fluid consumption, fluid loss, or physiological strain during 60min of moderate intensity exercise in the heat.