Postexercise rehydration in man: The effects of osmolality and carbohydrate content of ingested drinks

Abstract

Objective This study investigated the effect of the osmolality and carbohydrate content of drinks on their rehydration effectiveness after exercise-induced dehydration. Methods Six healthy male volunteers were dehydrated by 1.9 ± 0.1% of body mass by intermittent cycle ergometer exercise in the heat before ingesting one of three solutions with different carbohydrate contents and osmolalities over a period of 1 h. Thirty minutes after the cessation of exercise, subjects drank a volume that amounted to 150% (130–150, median [range]) of their body mass loss. Drinks contained 25 mmol/L Na + and 0%, 2%, or 10% glucose with osmolalities of (mean ± SD) 79 ± 4, 193 ± 5, and 667 ± 12 mosm/kg, respectively. Blood and urine samples were collected before exercise, after exercise, and 0, 1, 2, 3, 4, and 6 h after the end of the rehydration period. Results Significantly more of the ingested fluid was retained in the 10% trial (46 ± 9%) than in the 0% trial (27 ± 13%), with 40 ± 14% retained in the 2% trial. Subjects remained euhydrated for 1 h longer in the 10% glucose trial than in the 2% glucose trial. In the 2% glucose trial, plasma volume was elevated immediately after and 1 h after rehydration. Conclusion This study suggests that, following the rehydration protocol used, hypertonic glucose-sodium drinks may be more effective at restoring and maintaining hydration status after sweat loss than more dilute solutions when the sodium concentration is comparable.