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 °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 (EUH(FL) and HYPO(FL); 10 min ad libitum consumption) or no fluid replacement (EUH(NF) and HYPO(NF)). 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 (HYPO(FL), 3.0% ± 1.2%; HYPO(NF), 2.6% ± 0.6%) compared to EUH (EUH(FL), 0.2% ± 0.7%; EUH(NF), 0.6% ± 0.5%) trials (p < 0.001). Following recovery, there were no differences in %BML between HYPO(FL) and HYPO(NF) (p > 0.05) or between EUH(FL) and EUH(NF) (p > 0.05). Beginning at minute 5 during the recovery period, thirst perception was significantly greater in HYPO(NF) than EUH(FL), EUH(NF), and HYPO(FL) (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.