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

Abstract

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.

Keywords: assessment; exercise; fluid replacement; hypohydration; perception.

Figure 1

(A) Thirst perception throughout exercise and post-exercise recovery and (B) delta change (recovery–exercise) of pooled means in thirst perception (TH) by trial × condition. # indicates a significant difference between HYPO_FL and HYPO_NF, EUH_FL, and EUH_NF, p < 0.05. EUH_FL = minimized fluid losses during exercise and remaining losses replaced during recovery; EUH_NF = minimized fluid losses during exercise and did not replace losses during recovery; HYPO_FL = fluid restricted during exercise and losses replaced during recovery; HYPO_NF = fluid restricted during exercise and losses not replaced during recovery.

Figure 2

Perceptions of (A) thirstiness, (B) dryness, (C) pleasantness, (D) fullness, (E) taste, and (F) sickness in EUH_FL EUH_NF HYPO_FL and HYPO_NF groups. * indicates a significant difference between the HYPO trial (HYPO_FL and HYPO_NF) and EUH trial (EUH_FL and EUH_NF); p < 0.05. EUH_FL = minimized fluid losses during exercise and remaining losses replaced during recovery; EUH_NF = minimized fluid losses during exercise and did not replace losses during recovery; HYPO_FL = fluid restricted during exercise and losses replaced during recovery; HYPO_NF = fluid restricted during exercise and losses not replaced during recovery.

Figure 3

Changes in (A) rectal temperature and (B) heart rate during exercise and recovery in EUH_FL, EUH_NF, HYPO_FL, and HYPO_NF groups. EUH_FL = minimized fluid losses during exercise and remaining losses replaced during recovery; EUH_NF = minimized fluid losses during exercise and did not replace losses during recovery; HYPO_FL = fluid restricted during exercise and losses replaced during recovery; HYPO_NF = fluid restricted during exercise and losses not replaced during recovery.