Thirst Perception Tracks Progressive Dehydration During Exercise In The Heat

Abstract

Thirst is claimed to be a perfect measure of fluid needs, but insufficient information is available on the association between thirst perception and actual dehydration. Purpose: to assess the strength of the actual association between net fluid balance (NFB) and thirst during exercise in the heat. Methods: Fourteen healthy participants (27.3 ± 2.3 years old, 72.55 ± 18.52 kg; mean ± standard deviation) reported to the laboratory after an overnight fast and completed two different sessions (dry heat and humid heat), equivalent in WBGT (27.7°C), one week apart. Participants exercised for 2 hours on a stationary bicycle in a climate-controlled chamber without any fluid intake. Nude and dry BM was measured every 30 minutes; dehydration was calculated from weight loss as %BM. At the same time points, thirst perception (TP) was evaluated with Engell’s 9-point scale. Means were compared via one- or two-way ANOVAs as pertinent. A multiple regression analysis was used to test the association between NFB and TP, with individuals included in the model. Results: initial values were consistent between sessions (BM: 72.5 ± 18.52 vs 72.26 ± 18.32 p = 0.185; USG: 1.017 ± 0.005 vs 1.017 ± 0.005, p = 0.77, and thirst: 2.6 ± 1.9 vs 2.4 ± 1.33, p = 0.39). Neither TP (p = 0.916) nor NFB (p = 0.140) were different between sessions, but both changed significantly over time (p < 0.001), see table. There was a clear association between thirst and net fluid balance during dehydration: R 2 = 0.74, R 2 a = 0.70; p < 0.001.