Effects Of Preexercise Rehydration Beverages On Fluid Balance And Exercise Tolerance

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Decreases in plasma and intracellular water volumes during exercise may decrease sweat rate, promote hyperthermia, and increase the rate of glycogen utilization. Rehydration beverages containing electrolytes and carbohydrates may increase water intake during exercise and limit water excretion in urine. PURPOSE To study the efficacy of 4 preexercise beverages on fluid balance during submaximal exercise and subsequent exercise performance. METHODS Twenty healthy people (10 male, 10 female; 24±3 y) exercised at 57±4% (mean±SD) VO peak in a thermoneutral environment (WBGT= 16.2±1.6 °C) for 90 min, 45 min after ingesting 355 ml of either chicken noodle soup (SOUP), a carbohydrate/electrolyte beverage (CE), or water (WATER). Water intake during exercise was allowed ad libitum except in a second soup trial (SOUPCON) where water was given at times and volumes equal to CE. After 90 min of steady state exercise subjects performed a time trial in which they accumulated as rapidly as possible the amount of work equal to 30 min at ∼60% VO2peak. Results: Total body mass lost and urine output were similar between trials. The additional water ingested during SOUP, CE, and SOUPCON (p<0.01) compared to WATER resulted in enhanced fluid balance in SOUP and SOUPCON compared to WATER and CE (−268±414 g and −328±500 g vs. −654±577 g and −477±596 g respectively, p<0.05). The percent change in plasma volume was not different in any trial. Plasma sodium was similar in all trials (p=0.8). Plasma osmolality (p=0.01) was higher during SOUPCON compared to CE and WATER at before and during exercise (P<0.05) and was higher in SOUP compared to WATER and CE at the end of exercise (p<0.05). Urine specific gravity increased in CE, WATER, and SOUPCON (p<0.05 for all). Urine osmolality decreased in CE and increased in SOUPCON (p<0.05), and total urinary output of sodium and potassium was higher in SOUPCON compared to CE (p<0.05). Heart rate, systolic and diastolic blood pressures, rectal temperature, and thirst responses were not different between trials. No performance differences were observed in the time trial (p=0.4). CONCLUSIONS Higher electrolyte concentrations associated with chicken noodle soup (S and SOUPCON) resulted in better maintenance of fluid balance due to increased water intake and less urinary water loss. Fluid balance differences did not result in significant differences in percent plasma volume, heart rate, blood pressure, body temperature regulation, or subsequent exercise performance. Supported Campbell Soup Co, Inc.