Ad libitum adjustments to fluid intake during cool environmental conditions maintain hydration status during a 3-day mountain bike race.

摘要

OBJECTIVE: In this study, the hydration status of amateur cyclists who voluntarily adjusted their fluid intake to environmental conditions during a 3-day, 248-km mountain bike (MTB) race was assessed. DESIGN: Prospective observational field study. SETTING: Sani2C MTB Race, KwaZulu-Natal, South Africa, 2006. PARTICIPANTS: 18 randomly selected amateur, male MTB cyclists. MAIN OUTCOME MEASURES: Reported usual fluid intake, environmental conditions, voluntary fluid intake, urine voided, changes in body mass, serum osmolality (SO), sodium concentration [Na(+)] and urinary specific gravity (Usg) during each stage (S). RESULTS: Dry bulb temperature (adjusted for windchill) ranged from 6 degrees to 21.4 degrees C during S1, S2 and S3. While 77.8% (n = 14) of subjects reported a usual intake of >750 ml h(-1) in previous MTB events, mean (SE) fluid intake in this race ranged from 341 (32) ml h(-1) during S1 to 551 (56) ml h(-1) during S3. Changes in mean body mass ranged between -0.99% and -2.02% during the three stages. Mean SO and serum [Na(+)] ranged between 292 (0.73) mOsm kg(-1) and 298 mOsm kg(-1) and 137 (0.35) mEq and 140 (0.42) mEq, respectively, during the 3-day period, while Usg remained