A randomized trial on thirst satiation during exercise in the heat: Effects on thermal strain, perceived concentration, and executive function

Background Oral rehydration reduces thirst sensation, which potentially influences cognitive performance. Aim This study examines whether thirst influences cognitive performance between intravenous and oral rehydration. Methods Twelve men cycled for 90 min at 55% VO 2max in 35°C and 30% r.h, followed by a 12 km cycling time trial. Two experimental trials were conducted: participants consumed 25 mL of water every 5 min (low thirst: LT) or were infused with 25 mL of isotonic saline every 5 min via intravenous tube (high thirst: HT). Thirst was measured every 5 min with visual analog scales. The Environmental Symptoms Questionnaire (ESQ), Profile of Mood States (POMS), a modified flanker task, body mass, and urine specific gravity (USG) were recorded before and the end of each trial. Summary There were no significant differences in body mass loss and USG ( p ≥ 0.14), demonstrating similar hydration states. Thirst was higher in HT compared to LT after 15 min and throughout the 90 min and 12 km time trial ( p = 0.006). Participants reported feeling performance decrements (mean ± SD; HT: 3.7 ± 0.2, LT: 3.1 ± 0.3, p = 0.012), difficulty concentrating (HT: 1.8 ± 0.2, LT: 1.4 ± 0.1, p = 0.032), and an overall heightened subjective thermal strain (total ESQ, HT: 27.3 ± 1.1, LT: 24.8 ± 1.0, p < 0.045) during HT trials compared to LT for the ESQ. No significant differences were observed in the flanker task and POMS between trials ( p > 0.05). Thirst may not affect executive function performance, though it may increase subjective thermal strain during exercise in the heat. This study suggests that strategies for mitigating thirst are as important as maintaining hydration status to maintain concentration and subjective thermal strain.