Date of Completion


Embargo Period



Hydration, Hypohydration, Thirst, Exercise, Hyponatremia

Major Advisor

Douglas J. Casa

Associate Advisor

Lawrence E. Armstrong

Associate Advisor

Elaine C. Lee

Associate Advisor

Lindsay J. DiStefano

Field of Study



Doctor of Philosophy

Open Access

Open Access


The purposes of these investigations were to describe the relationship of thirst to hydration during exercise, and to determine the impact of fluid volume on thirst following exercise. Eleven males completed four treadmill exercise trials of up to 180 minutes in a warm environment (35°C, 30% RH), then a 1-hour seated recovery. Two trials began euhydrated, and two hypohydrated. Fluid was given in one trial during exercise to match sweat rate. During recovery, participants were grouped to receive either a Small (1% of body mass (BM)) or Large (4% of BM) fluid bolus. Immediately post-exercise (IPE), there was a relationship between Thirst and body mass loss (BML) (p<0.008) and BML% (p<0.009). Moderate-high thirst was significantly related to IPE plasma osmolality (POsm; R²=0.142, p=0.037). There was a significant relationship between low change in thirst and IPE POsm change (R²=0.317, p=0.010), Copeptin change (R²=0.212, p=0.041), and BML (R²=0.325, p=0,009) and BML% (R²=0.356, p=0.006). IPE thirst was correlated with IPE POsm (ρ=0.600, p<0.001), BML% (ρ=-0.644, p<0.001), and plasma volume change (ρ=-0.326, p=0.040). HyR trial fluid bolus in the Large group (2±1) resulted in lower Thirst than the Small group (7±2, p<0.001) after recovery. Large group only consumed fluid to replace 3.84±1.73% BML. There is a relationship between a low level of thirst and hydration before exercise, and a higher level of thirst and hydration after exercise. Fluid bolus decreased thirst to such a degree that body mass loss replacement was incomplete.