Ad libitum Adjustments to Fluid Intake in Cool Environmental Conditions Maintain Hydration Status in a Three-Day Mountain Bike Race

¹ University of KwaZulu-Natal, South Africa

^* To whom correspondence should be addressed. E-mail: futree{at}ukzn.ac.za.

Accepted 19 May 2008

	Abstract

Objective: To assess the hydration status of amateur cyclists who voluntarily adjusted their fluid intake to environmental conditions in a three-day, 248 km mountain bike (MTB) race

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 - 21.4°C during S1, S2 & S3. While 77.8 % (n =14) of subjects reported a usual intake of >750 ml. hr^-1 in previous MTB events, mean (±SEM) fluid intake in this race ranged from 341 (±32) ml. hr^-1 during S1 to 551 (±56) ml. hr^-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) and 298 mosm.kg^-1 and 137 (±0.35) and 140 (±0.42) meq., respectively, during the three-day period, while Usg remained 1.025.

Conclusion: Ad libitum fluid intake during the 2006 Sani2C MTB Race which took place in unexpectedly cold environmental conditions, was slightly below current recommendations and substantially lower than the usual reported fluid intake of subjects. Changes in body mass, SO, serum [Na⁺] and Usg were not clinically significant, indicating that adequate an hydration status was maintained during the multi-day MTB cycle race.