Thirst perception has been studied as an indicator of acute dehydration during exercise, however, as a perception, it could be affected by the information received about water (sweat) losses.

PURPOSE: To identify if thirst perception (TP) can be affected by knowledge of water losses during exercise.

METHODS: 11 males exercised intermittently in the heat on two occasions (30 min bicycle-30 min treadmill, at 70-80%HRmax), to a dehydration of 3.9±0.4% and 3.8±0.4% body mass (BM). TP and heat sensation were measured every 30 minutes during exercise. During session one (S1) they received real information about their water losses; in session two (S2), they received false information about their water losses (60% of their real losses). Information was given every 30 minutes; the order of the sessions was randomly assigned. After finishing the exercise, they ingested water ad libitumfor 30 minutes. Urine osmolality was measured preexercise, postexercise and at the end of each trial. Data were analyzed using Student’s t and analysis of variance, as appropriate.

RESULTS: Preexercise conditions were not statistically different between sessions (Table).

Table: Exercise time was the same (115±22.3 and 110±24.4 min, t=-1.27; p=0.232). Thirst perception between sessions was also similar (48.26±2.11 and 51.2±3.81, for S1 and S2, respectively; f=0.661; p=0.447). Thirst percepton changed sigificantly over time in both sessions (f=44.6; p= 0.001), but no interaction (f=0.382; p=0.559). Power analysis for TP was 79%. Heat sensation showed no differences between sessions (8.14±2.18 and 6.00±0.23, for S1 and S2; f=0.982; p=0.360) or over time (f=2.88;p=0.140). Uosm was not different between sessions 659.94±80.59 and 636.09±79.76, for S1 and S2; f=0.134; p=0.722). Water ingestion was the same between sessions (1220.4±248.6 mL and 1228±421.8 mL; t=-0.66, p=0.949).

CONCLUSION: these results suggest that thirst perception is not affected by knowledge of water losses during exercise.