Hydration Habits Following Repeated Exercise In The Heat

BACKGROUND: Exposure to heat expedites the anticipated rise of core temperature during exercise. As body temperature increases, continued exercise may become uncomfortable, resulting in greater perceived exertion. Consuming water during exercise allows for an increased sweat response, which will contribute to delayed increases in core temperature, thus limiting increases in perceived exertion, and increasing voluntary exercise. PURPOSE: To compare water intake and perceived exertion between an initial and repeated exercise trial in a hot condition. METHODS: Thirty moderately trained men (22±3 yrs, 3.6± 0.9 L•min-1) completed two exercise sessions of 90 minutes of cycling at 60% VO2max in a hot condition (35 °C). Each trial was separated by two weeks. Upon arrival, participants provided a urine sample to confirm hydration via urine specific gravity assessment (USG < 1.125). Prior to entering the environmental chamber, participants were provided a pre-weighed water bottle. Every five minutes during exercise, the bottle was weighed and then replaced with a new pre-weighed bottle. Every 10 minutes, participants were also asked to rate their perceived exertion (RPE) via Borg’s scale. Water intake was summed in 10-minute intervals and changes in drinking behavior were analyzed via repeated measures analysis of variance (ANOVA) between trial and time. A cumulative sum of water intake during each 10-min interval was also calculated and correlated with RPE. RESULTS: Water intake was not different between trials (F=0.108, p=0.744, ηp2=0.004) or over time (F=1.695, p=0.156, ηp2=0.055). RPE displayed an anticipated increase over time (F=90.157, p<0.001, ηp2=0.818) and a nonsignificant difference between trials (F=4.204, p=0.054, ηp2=0.174). Lastly, correlational analysis indicated that water intake was not related to RPE. CONCLUSIONS: It is possible that the experienced population enrolled in this investigation would not alter water intake between two identical exercise trials or over the duration of exercise. As expected, RPE increased during exercise, without a difference between trials. The absence of a relationship between water intake and RPE may be explained by the lack of increase in intake over time and/or by the potential that trained individuals may readily expel heat, regardless of water intake. DSM i-Health, Inc.