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. PURPOSETo 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±0.5 °C). METHODTen elite, heat-acclimatized, male endurance cyclists (30±5 y, 76.5±7.2 kg, 1.81±0.07 m, VO2peak61.3±5.2 ml[BULLET OPERATOR]min[BULLET OPERATOR]kg, body fat10.5±3.3%, Powermax392±33 W) performed three sets of criterium-like cycling, consisted of a 5-km at 50% power max, followed by a 5-km all out at 3% grade (total 30 km). Participants rode the course on two separate occasions and in a counter balanced order, either during ad libitum drinking (ADdrink water as much as they wished) and prescribed drinking (PDdrink water every 1 km to much fluid losses). To design the fluid intake during PD participants performed a familiarization trial to calculate fluid losses. RESULTSFollowing 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. Mean cycling speed for the 3rd bout of the 5 km hill cycling was greater in PD (30.2±2.4 km[BULLET OPERATOR]h) than in the AD trial (28.8±2.6 km[BULLET OPERATOR]h), by 5.1±4.8% (P