Research
Mixed
Dehydration of 2% body weight impairs endurance performance and increases cardiovascular strain in hot environments (>30°C), whereas it may be tolerated without significant performance loss in cold or temperate environments.
In hot weather, drink to match your sweat rate to avoid performance loss and heat injury. In cool or temperate weather, you can safely allow yourself to lose up to 2% of your body weight without expecting a significant drop in performance, which may be more practical than trying to drink large volumes while exercising.
GoodConditionalHIGH confidence
However, when exercising in a hot environment (>30°C), dehydration by 2% of body weight impairs absolute power production and predisposes individuals to heat injury... when the environment is cold (e.g. 5–10°C) or temperate (e.g. 21–22°C)... some athletes might tolerate body water losses amounting to 2% of body weight without significant risk to physical well-being or performance
Why this rating
Based on multiple controlled laboratory studies and field observations cited.
Source
Fluid and fuel intake during exercise
Edward F. Coyle · Journal of Sports Sciences · 2003
DOI 10.1080/0264041031000140545
narrative_reviewCited 406×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
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