Pre-Exercise Hydration Modulates the Sweat Rate and Executive Control during Moderate Exercise to 3% Dehydration under Thermoneutral Conditions

, 95% CI 0.04-0.63) and were more likely to reach 3% mass loss (10/16 vs. 1/14; p = 0.002). Despite greater sudomotor output, early Tc burden (0-90 min) did not differ between groups. Hydration status selectively affected executive control: Stroop naming interference showed a time × status interaction (F(1,27) = 4.57, p = 0.042), driven by slowing in HYP participants (≈+63 ms, p = 0.029), whereas Corsi indices were unchanged. These findings support targeting euhydration before prolonged exercise (e.g., morning USG <1.018), as inadequate baseline hydration may impair inhibitory control even when early Tc responses are comparable. Accordingly, for training or competition requiring rapid decision-making and attentional control, pre-exercise hydration strategies (planned fluid intake and/or USG-based monitoring) may be warranted to mitigate decrements in executive function.