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 1h. 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 6h 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 1h longer in the 10% glucose trial than in the 2% glucose trial. In the 2% glucose trial, plasma volume was elevated immediately after and 1h 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.