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What To Drink Before/During Running
Most sports drinks on the market are what sports scientists call isotonic, which means they contain a carbohydrate solution that is at 6-8% concentration. These drinks are in the middle of the spectrum in terms of absorption rate, with water being the most readily absorbed (hypotonic) and something like fruit juice, being greater than 8% sugar concentration (hypertonic) and therefore the least absorbable. Because the sugar concentration of most sports drinks is higher than that of most body fluids, they are not readily absorbed into the blood stream and are thus not optimal for the purpose of hydration.
Before and during a run, rehydration should be your main priority. When training in warm conditions, rehydration will allow you to maintain fluid balance and stay cool. Accordingly, your best choice before and during your run would be water, a heavily diluted sports beverage, or water with electrolyte tablets.
By drinking water alone, diluting your sports drink, or using electrolyte substitutes, you provide your body with the best combination of electrolyte replacement and immediate absorption. Likewise, electrolytes, especially sodium and potassium, reduce urine output, speed the rate at which fluids empty the stomach, promote absorption from the small intestine, and encourage fluid retention.
Furthermore, not only do you want to shy away from consuming unnecessary amounts of simple sugar when you can avoid it, research shows that when a runner consumes high-glycemic (Gl) foods such as high-sugar sports drinks or energy bars an hour before a run, he or she may become fatigued more quickly.