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Programmed vs. Thirst-Driven Drinking during Prolonged Cycling in a Warm Environment.

David Jeker1, Pascale Claveau1, Mohamed El Fethi Abed1

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Programmed fluid intake (PFI) improved cycling power output compared to thirst-driven fluid intake (TDFI) during prolonged exercise in heat. PFI may benefit endurance athletes by optimizing performance when urination time is not a concern.

Keywords:
cyclingendurance performancefluid balancehydrationprolonged exercisethirst

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Area of Science:

  • Exercise Physiology
  • Sports Nutrition
  • Environmental Physiology

Background:

  • Fluid balance is critical for endurance athletes, especially during prolonged exercise in hot conditions.
  • The optimal hydration strategy, programmed vs. thirst-driven, for maximizing performance and minimizing exercise-associated muscle cramps (EAMC) remains debated.
  • Previous research suggests dehydration can impair performance and potentially contribute to EAMC.

Purpose of the Study:

  • To compare the effects of programmed fluid intake (PFI) versus thirst-driven fluid intake (TDFI) on prolonged cycling performance.
  • To investigate the impact of PFI and TDFI on the incidence of exercise-associated muscle cramps (EAMC) in endurance athletes.
  • To determine the optimal fluid intake strategy for cyclists during extended, high-intensity efforts in the heat.

Main Methods:

  • Eight male endurance athletes completed two 5-hour cycling trials at 61% V˙O2peak in 30°C/35% humidity, followed by a 20 km time-trial (TT).
  • Fluid intake was manipulated: PFI aimed to limit body mass loss to 1%, while TDFI was based on perceived thirst.
  • EAMC was assessed post-TT using maximal voluntary isometric contractions; body mass loss and TT power output were measured.

Main Results:

  • Body mass loss was not significantly different between PFI (1.5 ± 1.0%) and TDFI (2.5 ± 0.9%).
  • Mean power output during the 20 km TT was significantly higher with PFI (278 ± 41 W) compared to TDFI (263 ± 39 W).
  • Total TT performance time was similar between conditions, and EAMC prevalence was comparable.

Conclusions:

  • Programmed fluid intake, targeting <2% body mass loss, enhances cycling power output during prolonged exercise in the heat when high intensity is required.
  • Thirst-driven fluid intake may lead to greater dehydration and reduced performance in similar conditions.
  • Athletes may benefit from PFI for performance optimization in events where urination breaks do not significantly impact overall time.