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Proper Hydration for your Half Marathon or Marathon

Proper Hydration for your Half Marathon or Marathon


Mark Halstead, MD

Marathon and Half Marathons can be a grind. If you are like most runners, you will take a minimum of 2 hours to complete a half marathon and over 4 hours to complete a full marathon. That’s a lot of time of continuous exercise and your body will need fuel and water to keep performing at its best throughout the race.

So, what is the best way to hydrate? There are lots of recommendations out there and everyone’s body is a little different so it really comes down to individualizing race hydration, to some extent.

One method that is no longer recommended is to drink, drink and drink some more during a race, even if you aren’t thirsty. That method had been proposed in the past but it may result in a dangerous outcome. If one drinks too much water during a race, often greater than 28 ounces per hour, you may dilute the salt (sodium) in your blood stream which can lower your blood sodium level and create something called hyponatremia. If the sodium level gets too low in our body it can lead to someone feeling very confused, can lead to seizures, and potentially even death. A good rule of thumb is you should not lose more than 3% of your body weight during a race and definitely should not gain weight during a race, which would imply you have taken in too much fluid.

Because of this problem, it is generally recommended to drink to your thirst level but not avoiding water altogether. Drinking more than 28 ounces an hour likely will result in your stomach not feeling very good as the extra fluid will likely slosh around in your stomach. Ideally, some of that fluid is taken in as a sports drink, which has some easily digestible carbohydrates and electrolytes that often your body will want during the race.

One should also know that the ‘carbo loading’ prior to a race has an extra benefit as those carbohydrates can help store water making them accessible to the body as they are used for fuel during your race.

So, use the water and sport drink stations during your run. When you do stop, also be sure to thank those volunteers for spending their time supporting you and your fellow runners during their race! They are trying to make your race the best it can be, so make them feel appreciated as well!

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