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Be sure to drink both early and often

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Question: Is it best to drink plain water or an "aid" drink when exercising in the summer? How much fluid (whichever is best) should I drink?

Answer: This is a fairly complex question that many scientists have studied . The general guideline is to drink enough to avoid becoming dehydrated. Dehydration hinders performance and can be extremely dangerous to your health. The American College of Sports Medicine has released a position statement on fluid replacement based on the latest scientific research and I will draw form this statement for many of my recommendations .

First, drink plenty of fluid before exercise (or work). It is a good idea to drink adequate fluids during the 24 hours before any competition or event, and drink about a pint of fluid 2 hours before to promote adequate hydration and allow time for excretion of excess fluid. Several studies have shown that dehydration decreases performance, and that drinking prior to the event improves performance.

Second, during exercise, athletes should start drinking early and at regular intervals to keep from dehydrating as they work. The amount needed depends on the heat and the intensity of the activity. For instance, maximum sweating rates can be as high as 3.5 liters an hour for well-trained, highly motivated athletes. But for most exercisers, a liter (about a quart) an hour will usually keep us hydrated (a cup every 15 minutes). The problem is that we need to drink whether we feel thirsty or not, because the thirst mechanism usually won't keep us hydrated enough.

Third, water is probably as good as an aid drink for exercise lasting less than an hour. However, any step that can help increase voluntary fluid intake will help; and several studies have shown that drinking sports drinks, with their flavoring and sweetness, increases voluntary fluid intake. And another study showed that a sports drink improved performance in a 50-minute exercise test, probably because of the glucose content.

Fourth, sports drinks are helpful for exercise bouts longer than an hour. This finding has special meaning for persons who have to work all day in the heat. The reason sports drinks are good for longer bouts of work relates to the glucose content, which provides an important source of energy. It also relates to sodium, which makes the fluid more palatable, helps replace sodium lost in the sweat and stimulates thirst so that enough fluid is ingested.

Fifth, sports drinks are helpful for rehydration following exercise. The problem with water after exercise is that it can actually suppress thirst and increase urine output. Sports drinks with sodium help maintain the thirst mechanism. It is a good idea to weigh yourself before and after exercise int he heat and replace the lost fluid with at least a pint for every pound of weight that is lost.