Hydration & Fueling in Distance Running

Hydration during exercise is a major factor in your performance. When it’s hot and/or you are working hard, your body wants to keep itself cool. To do that, it produces sweat. The amount that you sweat (how hard your body needs to work to keep you cool) depends on genetics, heat, and your effort level. When you sweat, you are not only losing water, but the electrolytes sodium, potassium, calcium and magnesium.

You begin to feel thirsty when your body has lost fluid (water) from the blood stream to cool itself, which causes the concentration of other components to shift. You brain sends the signal that you are thirsty to encourage you to drink for water to bring the body back in to balance. If you wait until you have a thirst signal, you have already started working towards dehydration. You can see a reduction in performance with as little as a 1% loss of body weight via sweat.

If you enjoy data, you can determine how much fluid you will typically lose during exercise by weighing yourself, nude, prior to 60 minutes of running. Weigh yourself, immediately following, also nude and note the amount of weight lost. For every pound lost in 60 minutes, you need ~16 oz of fluid to replace the loss. You can use this activity in different settings to determine what your typical sweat rate is, and begin to use this as an equation to determine how much fluid you need to replace while running to truly remain hydrated. Some elites will use this strategy, and then tweak their fluids to attempt to have no weight loss during long runs. *Note here that this is purely fluid loss, not physical weight loss. If you are someone who is trigged in any way by the scale, DO NOT use this strategy.

To remain hydrated, you should be taking in fluids at least every 15 minutes on a long run. If you are someone who has a typical sweat loss of 2 lbs in 60 minutes of activity, this equates to 32 ounces, or 8 ounces every 15 minutes. This influx of fluids, in a bolus, can lead to stomach discomfort and nausea. While you can build your body up to handling this, a better strategy would be to sip 2-4 ounces every 7-10 minutes.

Sweat isn’t simply water. It’s also electrolytes, which is why products like NUUN (no calories) and Gatordate (calories from carbohydrates) are so popular. Gatorade, and other calorie-containing sports drinks, can be useful because they contain carbs. The average person needs 30-60 grams of carbs per 60 minutes of running. For runners running longer than 2 hours, that need increases to 60-90 grams per hour later in the run because of depleted energy stores. Not all runners can tolerate multiple gels (which each contain about 25 grams of carbs), so sports drinks can come to the rescue. By alternating sports drinks and water you can get additional carbs, as well as fluids and electrolytes.

To implement this level of hydration, you have to practice. Going from 0 fluid intake to 32 ounces in one run will leave you doubled over with nausea. Instead, increase your intake slowly until you find your optimum replacement level. Your body will get used the fluid volumes over time, requiring you to drink less often as you will need to initially. You also have to figure out how to have those fluids available. Simply Hydration bottles tuck into your sports bras and shorts easily, without being uncomfortable. Handheld bottles can be useful, once you get used to carrying them. I also like to find safe locations to leave bottles. This can include running in loops where you can pick up a bottle from your driveway, asking a friend to set out a water bottle if you run past their house, or knowing where water fountains are.

In the days before a long run or race, don’t run into over hydration issues, either. Use your urine to evaluate if you are adequately hydrated. You urine should be a pale yellow. If it is dark yellow, you need more fluids. If it is completely clear, you are over-hydrated which can lead to nausea on electrolyte imbalance on race day.

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  • Heather Larson R.D.


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