The negative effects of dehydration on health and performance are well documented, but hydration practices during exercise in the heat vary widely among athletes and physically active people; many allow themselves to become dehydrated, while others drink too much for their needs, with potentially negative consequences. There is little research on how personal beliefs and subjective feelings, such as the fear that drinking before or during exercise will cause exercise-related transient abdominal pain (STITCH), influence drinking behavior during exercise.
PURPOSE: To assess fluid balance (FB) during moderate exercise in the heat and its association with beliefs regarding drinking fluids and other perceptions during exercise. METHODS: 93 physically active male college students exercised at 60% HRmax reserve for one hour. Each subject alternated stationary cycling, stair climbing, and Nordic Track® skiing in an environmental chamber at 30°C, 70% rh (WBGT = 26.8°C). Voluntary fluid intake (FI) of a cold (8–16°C) sports drink was monitored. Subjects were weighed nude and dry before and after the exercise session. Perceived importance of hydration (IMP) and actual practices, as well as side-stitch beliefs, were evaluated via questionnaire; perception of ambient HEAT, beverage palatability (PAL), stomach fullness (FULL), and gastrointestinal distress (GIPAIN) were assessed at times 25 and 55 min.
RESULTS: Fluid balance was −0.14 ± 0.89% (mean ± SD) of initial body mass (bm) (range −2.38 to 2.84%), with a sweat rate (SR) of 1208.3 ± 381.7ml•h-1 and FI of 1132 ± 610 ml•h-1. FB was associated with FI (R2 = 0.73), SR (R2 = 0.08), and IMP (R2 = 0.07) (p<0.01), but not with STITCH, PAL, HEAT or GIPAIN (p>0.05). Overhydrated individuals (FB>0.3%bm) were shorter (p = 0.04) but not lighter (p = 0.33) than dehydrated subjects (FB<-0.3%bm). Their FI was much larger (1700.1 ± 610.7 vs 791.8 ± 451.4ml•h-1, p<0.0005), but their SR was only a little less (1112.8 ± 341.7 vs 1367.3 ± 415.4 ml•h-1, p = 0.01). No significant differences were found between subgroups in any other measure, including STITCH and IMP.
CONCLUSION: Overhydration was much more strongly associated with overdrinking than with low sweat rates while IMP was a marginally significant predictor of FB. To maintain proper fluid balance, individuals would be better off relying on an objective drinking plan based on their measured sweat rates than on subjective feelings. Supported by the Gatorade Sports Science Institute and UCR-VI-245-97-002.
