The Rules of Hydration

The Rules of Hydration


Remember when the only guideline for staying hydrated during exercise was to drink--and drink often? And plain water was the perfect sports drink?

Thanks to new insights on how our bodies process fluids and other nutrients while we're working up a sweat, the conventional wisdom on when and what to drink is evolving. But even though there are new rules, the objective remains the same: improved performance and optimal health.


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Let's look at some old and new views on hydration:


 Old rule 1: Drink ahead of your thirst.

     New rule 1: Drink according to your thirst.


A study from the Sports Science Institute of South Africa examined runners during workouts who were drinking sports drinks at different rates. In the first trial, the runners drank when they felt thirsty. In the second trial, the runners drank at a moderate rate (about 4oz. every 15-20 minutes), and in the third trial, the runners drank at a high rate (about 10oz. everything 15-20 minutes). There was no significant difference in core body temperature or finishing times between the three trials. However, the runners experienced severe stomach distress and couldn't finish the workout during the third trial. This suggests that drinking too much can affect your performance.

"The idea that thirst comes too late is a marketing ploy of the sports-drink industry." -Tim Noakes, M.D.

Thirst is not a perfect indicator of hydration. Just drink as your thirst dictates.


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             Old Rule 2: Aim to completely prevent dehydration

             New Rule 2: Aim to slow dehydration


Recent research reveals that drinking enough fluid during exercise to make up for what you lose through sweat is problematic. Here's why:

1. When athletes drink according to thirst, they usually replace only 60-70% of the fluid they lose, but studies show that this state of slight dehydration does not effect performance.

2. Drinking enough fluid to prevent weight loss is based on the false assumption that all the weight loss is from body fluid evaporating as sweat. However, recent studies show that a significant amount is actually due to the loss of water stored with fat and carbohydrate molecules, which is released from the muscles when these stores are converted to energy. This kind of fluid loss has no dehydrating effect because it doesn't reduce blood volume.

3. Drinking to completely prevent dehydration tends to dilute concentration of sodium and other electrolytes in the blood, especially during prolonged exercise of more than two hours. Electrolytes are dissolved minerals that regulate your body's fluids, helping create the electrical impulses essential to physical activity. When you sweat, you release more sodium than any other electrolyte.

Instead of drinking to replace the fluid you sweat out during exercise, aim for keeping thirst at bay. Respond to your thirst right away with small amounts of sports drink.


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            Old Rule 3: use either a sports drink or water for             hydration

            New Rule 3: Use a sports drink instead of water


New research concerning the risks of blood sodium dilution caused USA Track and Field to revise its hydration guideline. While the guidelines used to suggest that water and sports drinks were equally good choices for hydration during intense physical activity, it now states, "A sports drink with sodium and other electrolytes is preferred."

Sports drinks simply hydrate better than water does during intense exercise.



Last Updated: 3/03/2014