The Utility of Thirst as a Measure of Hydration Status Following Exercise-Induced Dehydration

The purpose of this study was to examine the perception of thirst as a marker of hydration status following prolonged exercise in the heat. Twelve men (mean +/- SD; age, 23 +/- 4 y; body mass, 81.4 +/- 9.9 kg; height, 182 +/- 9 cm; body fat, 14.3% +/- 4.7%) completed two 180 min bouts of exercise on a motorized treadmill in a hot environment (35.2 +/- 0.6 degrees C; RH, 30.0 +/- 5.4%), followed by a 60 min recovery period. Participants completed a euhydrated (EUH) and hypohydrated (HYPO) trial. During recovery, participants were randomly assigned to either fluid replacement (EUHFL and HYPOFL; 10 min ad libitum consumption) or no fluid replacement (EUHNF and HYPONF). Thirst was measured using both a nine-point scale and separate visual analog scales. The percent of body mass loss (%BML) was significantly greater immediately post exercise in HYPO (HYPOFL, 3.0% +/- 1.2%; HYPONF, 2.6% +/- 0.6%) compared to EUH (EUHFL, 0.2% +/- 0.7%; EUHNF, 0.6% +/- 0.5%) trials (p < 0.001). Following recovery, there were no differences in %BML between HYPOFL and HYPONF (p > 0.05) or between EUHFL and EUHNF (p > 0.05). Beginning at minute 5 during the recovery period, thirst perception was significantly greater in HYPONF than EUHFL, EUHNF, and HYPOFL (p < 0.05). A 10 min, ad libitum consumption of fluid post exercise when hypohydrated (%BML > 2%), negated differences in perception of thirst between euhydrated and hypohydrated trials. These results represent a limitation in the utility of thirst in guiding hydration practices.