The Influence Of Perception And Comfort On Fluid Rehydration Preference: A Pilot Study

Exercise-induced dehydration is linked to decreased performance and an increased risk of exertional heat illness. Individuals use various rehydration methods during exercise, including ad libitum (unrestricted fluid intake), drinking to thirst (DTT), and prescribed drinking (PD; Prescribed fluid intake to replace lost fluids through sweat). While PD offers a precise fluid replacement strategy, questions arise about fluid intake and potential physiological or perceptual (effort and comfort) differences between drinking methods during exercise in the heat. PURPOSE: Investigate fluid intake, physiological, and perceptual differences among ad libitum, DTT, and PD. METHODS: 6 individuals completed three heat tolerance tests (HTT; conditions 40°C,40% RH). Rehydration methods for HTTs were ad libitum first, DTT second, and PD third. PD was chosen for the third HTT to prevent expectations about fluid intake for DTT and ad libitum. Physiological variables included core body temperature (Tc) and % body mass loss (%BML). Assessed in each HTT were perceptual scales for effort (RPE; rating of perceived effort) and comfort (TS; thermal sensation, SD; stomach discomfort, TD; thirst drive). Participants were interviewed about their assessment of the drinking methods at the study's conclusion. Physiological and perceptual differences among the three drinking methods were assessed with one-way ANOVAs and post-hoc t-tests for any observed main treatment effect. A two-way ANOVA explored interaction effects of drinking method and time. RESULTS: There were no differences in drinking volume, Tc, %BML, TS, RPE, and SD among the three methods (all p > 0.05). However, ad libitum and DTT showed greater TD than PD (2.076 ± 1.258, 1.986 ± 1.559, and 1.236 ± 1.171, respectively; p < 0.001). The two-way ANOVA found no interaction effect of drinking method and time for any physiological or perceptual measurements (all p > 0.05). All measures showed a time effect, increasing over time (all p < 0.001).4 out of 6 participants favored the PD method, citing their perceived ability to effectively control thirst. CONCLUSION: This preliminary investigation suggests that, during exercise in the heat, fluid intake, physiological measures, and perceptual variables, except for TD, show no significant differences across tested drinking methods. Rocky Mountain ACSM