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

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

Vitamin C, neutrophil function, and upper respiratory tract infection risk in distance runners: the missing link.

Moderate submaximal exercise results in neutrophilia and enhanced phagocytic and oxidative capacity of neutrophils. It has been hypothesized, however, that during intensive exercise and periods of intensive training this pro-oxidative effect becomes suppressive. Vitamin C is widely recognized for its antioxidant function in extracellular fluid, and it has been shown to neutralize O2-, HOCl, and .OH and to attenuate the suppression of phagocytic function. Clinical manifestation of reduced neutrophil function following participation in ultramarathon races has, however, not been observed. Although neutrophils constitute 50-60% of leukocytes and although they are the first line of defense to bacteriological invasion, postrace episodes of upper respiratory tract infection (URTI) are not correlated with a decrement in the function of this individual parameter of immune function. The efficacy of Vitamin C supplements in reducing the incidence of postrace URTI symptoms, therefore, cannot be fully explained at this stage.

Muscle glycogen repletion during active postexercise recovery.

High-intensity intermittent bicycle exercise was used to deplete muscle glycogen levels by 70% and elevate blood lactate levels to greater than 13.0 mmol/l. Thereafter subjects either cycled with one leg for 45 min followed by 45 min of passive recovery (partially active recovery) or rested for 90 min (passive recovery). During the first 45 min of partially active recovery 1) blood lactate (P less than 0.05) and pH levels (P less than 0.05) returned more rapidly to preexercise values than during passive recovery, 2) the rate of net glycogen resynthesis (0.28 mumol . g-1 . min-1) was the same in both legs, and 3) muscle lactate levels were significantly lower (P less than 0.05) in the passive than in the active leg. Thereafter the rate of net muscle glycogen resynthesis was unchanged (0.26 mumol . g-1 . min-1) and lactate removal could theoretically account for only 18% of the glycogen resynthesized. Overall, the rate of muscle glycogen resynthesis and muscle lactate removal was not different from that measured during passive recovery. After high-intensity exercise 1) glycogen repletion is not impeded by light exercise, and 2) blood glucose is an important substrate for glycogen resynthesis.