Hydration 101: Guidelines for Fluids and Electrolytes During Exercise


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In part 2 of this blog series, I will dive into one of the more controversial issues in sports nutrition– hydration guidelines during exercise. In other words, how much and how often should you drink during exercise. I will also address the role of sports drinks in your training and races.

As mentioned in the previous post, for peak performance you should have a basic hydration plan before entering a competition. This plan should have been developed and tested in training, months ahead of your event. There should be NO surprises on race day.

The goal during exercise is to drink enough to prevent excessive water loss and maintain electrolyte balance in the working muscle cells.  Hydration becomes more important as your exercise duration increases.

Hydration recommendations during exercise can be quite variable depending on a bunch of different factors such as:

  • weather conditions
  • sweat rate
  • exercise duration & intensity
  • type of exercise
  • opportunities to hydrate
  • fitness level


How much should you drink during training sessions?

There has been a lot of debate on this question, because the sports drink industry has been driving the guidelines. Where do you think the idea that athletes should “drink ahead of thirst” came from…you guessed it the sports drink companies (or research funded by them).


Even as recent as 2009 the guidelines were to drink 8-10 ounces of fluid every 15 minutes during exercise. So that’s 40 ounces per hour…really. For MOST people that is way too much. For endurance athletes this led to an increased incidence of a condition called hyponatremia (sometimes called exercise-induced hyponatremia or EIH). I will discuss this topic in a future blog post.


We now realize that everyone needs an individualized hydration plan and the requirements aren’t as great as originally thought. In general, I recommend athletes consume 4-6 ounces every 15-20 minutes (~12-24 ounces per hour). I also suggest that if you are training or racing for several hours, you should NOT rely exclusively on water . Along with overdrinking, this too can cause problems because your body needs calories(see section below).


How Do You Calculate Sweat Rate?

For endurance athletes doing prolonged training sessions (≥ 2-3 hours) it’s difficult to balance fluid and electrolyte deficits.

Sweat rate varies from person to person due to body weight differences, genetic factors, heat acclimation ability and metabolic (energy production) efficiency.

How many of you out there are heavy sweaters? Me too–

Monitoring pre- and post-workout body weights following exercise is one way to establish how much fluid you should try to consume during your endurance sessions.

To do this, weigh yourself before you exercise. Time your workout and keep track of the amount of fluid you consume. By weighing yourself after you exercise, you can determine how much fluid you lost. This amount can be used to estimate how much fluid you need.


Follow the example below to calculate sweat rate:

a. Pre-exercise body weight      125 lbs
b. Post-exercise body weight    124.5 lbs
c. Change in body weight          -0.5 lbs (or 8 ounces)
d. Drink Volume                           22 ounces
e. Urine Volume                             0 ounces (subtract if you take a pit stop)

Follow the example below to calculate sweat rate
f. Sweat loss (c + d – e)               30 ounces
g. Exercise time                          1.5 hours
h. Sweat Rate (f ÷ g)       20 ounces/ hour

So a good place to start is 20 ounces/hour or 5 ounces/15 minutes

Tweak this volume as needed.


Water or Sports Drink: Which One Is Best?sports drinks vs. water

To sustain endurance performance ≥ 1 hour, carbohydrate consumption (with a mixture of sugars such as glucose, fructose, maltodextrin, and sucrose) may be beneficial.

Carbohydrate consumption at a rate of ~30-60 grams per hour has been shown to be quite effective in maintaining glucose levels for endurance exercise.

If you mix your own carbohydrate solution the concentration matters. It shouldn’t be more than a 6%-8% carbohydrate because anything over this may impede gastric (stomach) emptying and cause GI distress.

Electrolyte needs during prolonged exercise are best replenished with fluids containing 460-690 milligrams per liter of sodium and 80-200 milligrams per liter of potassium. Most sports drinks meet these guidelines so no worry there. The only issue would be if you made your own electrolyte replacement drinks (which isn’t hard at all).



The best hydration strategy during exercise is one that has been individualized to meet your needs. The guidelines provided above are a great starting point but it’s up to you to modify as needed.

Now it’s your turn. I’d love to here from you!

Tell me what you consume during your long runs of over an hour. There certainly are a lot of choices out there.

Nab a free PDF with my key hydration do’s and don’ts below.

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Learn the exact steps I used to become a 9x Ironman finisher, ultramarathoner, and Boston Qualifier. Take the guesswork out of race-day nutrition.

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