Title: Fluid Intake Sufficient to Replace Dehydration Attenuates Hyperthermia and Body Fluid Imbalance During Exercise
Abstract: 2145 PURPOSE: To examine the effect of fluid intake sufficient to replace dehydration attenuates hyperthermia and body fluid imbalance during high intensity exercise induced dehydration of approximately 2% per body weight (BW) without rehydration, in a hot environment. METHODS: Seven healthy male subjects cycled for 105min at 70% VO2max in a climatic chamber (32°C Ta, 60% RH, 27.7°C WBGT), while receiving no fluid intake (NF), ad libitum fluid intake (AD), fluid intake of 1% per BW (F1) and fluid intake of 2% per BW (F2). During AD, F1 and F2, carbohydrateelectrolyte beverage maintained at 5°C was ingested at immediately before exercise and at 15, 33, 51, 69 and 87min during exercise. Blood samples were corrected immediately before exercise and at 51 and 105min of exercise. Urine samples were corrected before and after exercise. RESULTS: After 105min of exercise, the degree of dehydration averaged 2.2, 1.1, 1.1 and 0.1% BW during NF, AD, F1 and F2, respectively. Rectal temperature (Tre) was significantly lower in F2 from 54 to 105min of exercise than those in NF (P<0.05), and we observed that dehydration linearly increased Tre by 0.41°C for each percent decrease in BW during exercise. In F2, heart rate was significantly lower from 33 to 105min of exercise than those in NF (P<0.05). Plasma volume in F2 was higher at 51min in exercise than those in NF and AD (P<0.05), and was higher at 105min of exercise than those in others (P<0.05). Serum osmolality at 105min of exercise was significantly lower in F2 than those in others (P<0.05). The decrease in urine flow rate (UFR) and urine to serum osmolality ratio (USosm) were graded in proportion to the degree of dehydration, although both UFR and USosm were not changed in each trial significantly. In F2, free water clearance (CH2O) was significantly lower than those in NF, and creatinine clearance (Ccr) and osmolar clearance (Cosm) were significantly higher than those in NF. We observed that dehydration linearly increased CH2O by 0.29 ml/min, decreased Ccr by 18.0 ml/min and decreased Cosm by 0.40 ml/min for each percent decrease in BW. CONCLUSIONS: These results demonstrate a graded impairment of thermoregulation, body fluid homeostasis and renal concentrating ability with increasing dehydration levels and/or with decreasing rehydration levels during high intensity exercise in a hot environment. Thus, fluid intake sufficient to replace dehydration during high intensity exercise in a hot environment provides a thermoregulatory and a body fluid regulatory advantage compared with fluid intake insufficient to replace dehydration.
Publication Year: 2004
Publication Date: 2004-05-01
Language: en
Type: article
Indexed In: ['crossref']
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