Mild dehydration and cycling performance during 5-kilometer hill climbing

Context: Hydration has been shown to be an important factor in performance; however, the effects of mild dehydration during intense cycling are not clear. Objective: To determine the influence of mild dehydration on cycling performance during an outdoor climbing trial in the heat (ambient temperature = 29.08C 6 2.28C). Design: Crossover study. Setting: Outdoor. Patients or Other Participants: Ten well-trained, male endurance cyclists (age = 28 6 5 years, height = 182 6 0.4 cm, mass=7364 kg,maximal oxygen uptake=5669mL-min ^-1-kg^-1, body fat=23% 6 2%, maximal power=354 6 48 W). Intervention(s): Participants completed 1 hour of steadystate cycling with or without drinking to achieve the desired preexercise hydration level before 5-km hill-climbing cycling. Participants started the 5-km ride either euhydrated (EUH) or dehydrated by -1% of body mass (DEH). Main Outcome Measure(s): Performance time, core temperature, sweat rate, sweat sensitivity, and rating of perceived exertion (RPE). Results: Participants completed the 5-km ride 5.8% faster in the EUH (16.6 6 2.3 minutes) than DEH (17.6 6 2.9 minutes) trial (t1=10.221, P=.001). Postexercise body mass was-1.4% 6 0.3% for the EUH trial and-2.2% 6 0.2% for the DEH trial (t1 = 191.384, P , .001). Core temperature after the climb was greater during the DEH (39.28C 6 0.38C) than EUH (38.88C 6 0.28C) trial (t1=8.04, P=.005). Sweat rate was lower during the DEH (0.44 6 0.16 mg-m^-2-s^-1) than EUH (0.51 6 0.16 mg-m ^-2-s^-1) trial (t8 = 2.703, P = .03). Sweat sensitivity was lower during the DEH (72.6 6 32 g-8C^-1-min^-1) than EUH (102.6 6 54.2 g-8C^-1-min^-1) trial (t8 = 3.072, P = .02). Lastly, RPE after the exercise performance test was higher for the DEH (19.0 6 1.0) than EUH (17.0 6 1.0) participants (t9 =-3.36, P = .008). Conclusions: We found mild dehydration decreased cycling performance during a 5-km outdoor hill course, probably due to greater heat strain and greater perceived intensity.