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Programmed vs. Thirst-Driven Drinking during Prolonged Cycling in a Warm Environment.
David Jeker1, Pascale Claveau1, Mohamed El Fethi Abed1
1Faculty of Physical Activity Sciences, University of Sherbrooke, Sherbrooke, QC J1K 2R1, Canada.
Nutrients
|January 11, 2022
Summary
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.
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.
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