programmed fluid intake -vs- make it up as you go along…….
“Drinking ad libitum during exercise often leads to dehydration…..”
“… study the effect of a prescribed hydration protocol matching fluid losses on a simulated 30-km criterium-like cycling performance in the heat….”

“10 elite heat-acclimatized male endurance cyclists 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 (drink water as much as they wished) or prescribed drinking (drink water every 1 km to match fluid losses).”
“The data suggested that prescribed drinking to match fluid losses during exercise in the heat provided a performance advantage because of lower thermoregulatory strain and greater sweating responses.”
Bardis, et al
Prescribed Drinking Leads to Better Cycling Performance than Ad Libitum Drinking
Medicine & Science in Sports & Exercise — Volume 49 #6 — June 2017 — page 1244