Blinded and unblinded hypohydration similarly impair cycling time trial performance in the heat in trained cyclists

Abstract

Knowledge of hydration status may contribute to hypohydration-induced exercise performance decrements; therefore, this study compared blinded and unblinded hypohydration on cycling performance. Fourteen trained, nonheat-acclimated cyclists (age: 25 5 yr; V O2peak: 63.3 4.7 ml·kg1·min1; cycling experience: 6 3 yr) were pair matched to blinded (B) or unblinded (UB) groups. After familiarization, subjects completed euhydrated (B-EUH; UB-EUH) and hypohydrated (B-HYP; UB-HYP) trials in the heat (31°C); 120-min cycling preload (50% Wpeak) and a time trial (~15 min). During the preload of all trials, 0.2 ml water·kg body mass1 was ingested every 10 min, with additional water provided during EUH trials to match sweat losses. To blind the B group, a nasogastric tube was inserted in both trials and used to provide water in B-EUH. The preload induced similar (P 0.895) changes in body mass between groups (B-EUH: 0.6 0.5%; B-HYP: 3.0 0.5%; UB-EUH: 0.5 0.3%; UB-HYP 3.0 0.3%). All variables responded similarly between B and UB groups (P 0.558), except thirst (P 0.004). Changes typical of hypohydration (increased heart rate, rating of perceived exertion, gastrointestinal temperature, serum osmolality and thirst, and decreased plasma volume; P 0.017) were apparent in HYP by 120 min. Time trial performance was similar between groups (P 0.710) and slower (P 0.013) with HYP for B (B-EUH: 903 89 s; B-HYP: 1,008 121 s; 11.4%) and UB (UB-EUH: 874 108 s; UB-HYP: 967 170 s; 10.1%). Hypohydration of ~3% body mass impairs time trial performance in the heat, regardless of knowledge of hydration status.