Training With Fluid Restriction Thrice A Week For Four Consecutive Weeks: Impact On Thirst Perception

It is still unknown how training with fluid restriction several times a week for several consecutive weeks impacts thirst perception (TP). PURPOSE: Examine how TP is impacted over 4 consecutive weeks while training 3 times per week with fluid restriction. METHODS: 12 individuals (9 men; 23 ± 5 yrs; 72 ± 13 kg; VO2max of 54 ± 6 mL/kg/min) completed 4 weeks of training while undergoing each week 3 training sessions (walking/jogging for (i) 1 h, until losing (ii) 2% or (iii) 4% body mass) with fluid restriction, each separated by 2-3 days. Each week, the 1 h exercise session was performed first, whereas the 2% and 4% exercise sessions were administered in a randomized crossover fashion. Exercise (55% VO2max) was conducted in a climatic chamber set at 40 °C, 20-30% relative humidity, with a simulated wind speed of ~5 km/h. Thirst perception was measured every 10 min with a 1-11 arbitrary scale, and made comparable across exercise sessions with a transformation based on % completion time. Data were analyzed using mixed linear models with 2 or 3 factors (conditions (CON): 1 h, 2%, 4%; training weeks (W); % completion time (T) within trials) and participants as random effect. RESULTS: Participants started all exercise sessions adequately and similarly hydrated as indicated by no significant W effect for mean % difference in body mass among exercise sessions (all <1%) and urine specific gravity (all ≤1.013 g/mL). Mean (± SD) exercise duration decreased significantly over W from 91.1 ± 41.8 (W1) to 83.8 ± 32.9 min (W4) and mean sweat rate increased significantly over W from 1.30 ± 0.34 (W1) to 1.42 ± 0.40 L/h (W4), but mean % body mass loss (1 h: 1.8 ± 0.3; 2%: 2.2 ± 0.2; 4%: 4.1 ± 0.2%) and mean total sweat loss (1.90 ± 0.8 L) did not differ significantly across W. Mean TP was different among CON (1 h: 3.8 ± 1.4; 2%: 3.4 ± 1.4; 4%: 4.5 ± 2.1, p < 0.01) and mean TP increased (p < 0.01) over T from 2.0 ± 0.7 (W1) to 5.5 ± 1.7 (W4). Mean TP decreased (p < 0.01) over W from 4.3 ± 1.8 (W1) to 3.6 ± 1.6 (W4), with intermediary values of 3.9 ± 1.7 (W2) and 3.7 ± 1.6 (W3). No significant (p values all >0.47) CON * W, T * W or CON * W * T were observed. CONCLUSION: In young individuals, training in the heat (2 sessions of ~60 min and 1 session of ~130 min) on 3 occasions per week with fluid restriction and body mass losses ranging from 1.8 to 4.1% will lead to a decrease in TP over a 4-week period.