Prescribed Drinking Leads to Better Cycling Performance than Ad Libitum Drinking

Drinking ad libitum during exercise often leads to dehydration ranging from -1% to -3% of body weight. Purpose This article aimed to study the effect of a prescribed hydration protocol matching fluid losses on a simulated 30-km criterium-like cycling performance in the heat (31.6 degrees C 0.5 degrees C). Methods Ten elite heat-acclimatized male endurance cyclists (30 5 yr, 76.5 +/- 7.2 kg, 1.81 +/- 0.07 m, VO2peak = 61.3 +/- 5.2 mLmin(-1)kg(-1), body fat = 10.5% +/- 3.3%, Power(max) = 392 +/- 33 W) performed three sets of criterium-like cycling, which consisted of a 5-km cycling at 50% power max followed by a 5-km cycling all out at 3% grade (total 30 km). Participants rode the course on two separate occasions and in a counterbalanced order, during either ad libitum drinking (AD; drink water as much as they wished) or prescribed drinking (PD; drink water every 1 km to much fluid losses). To design the fluid intake during PD, participants performed a familiarization trial to calculate fluid losses. Results After the exercise protocol, the cyclist dehydrated by -0.5% +/- 0.3% and -1.8% +/- 0.7% of their body weight for the PD and AD trial, respectively. The mean cycling speed for the third bout of the 5-km hill cycling was greater in the PD trial (30.2 +/- 2.4 kmh(-1)) compared with the AD trial (28.8 +/- 2.6 kmh(-1)) by 5.1% +/- 4.8% (P < 0.05). Gastrointestinal, mean skin, and mean body temperatures immediately after the last hill climbing were greater in the AD compared with the PD trial (P < 0.05). Overall, sweat sensitivity during the three climbing bouts was lower in the AD (15.6 +/- 5.7 gW(-1)m(-2)) compared with the PD trial (22.8 +/- 3.4 gW(-1)m(-2), P < 0.05). Conclusion The data suggested that PD to match fluid losses during exercise in the heat provided a performance advantage because of lower thermoregulatory strain and greater sweating responses.