Hydration for Runners: Measuring Your Sweat Rate

With highs around the country reaching above 100 degrees, hydration is vital to having a great run. For runners running more than 60 minutes, it is important to make sure you are properly hydrated and paying attention to how you are feeling during your runs (especially if you are running during the day or early evenings).

Measuring your sweat rate is one way to make sure you are properly hydrating during your runs. The formula and worksheet below can help you find out what your sweat rate is and how much fluid you should be consuming. Note that your sweat rate may change depending on the temperature and location of where you are running.

Total sweat rate = (1) Body weight pre-training – (4) Body weight post-training + (2) Fluid intake – (3) Urine volume)

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 (5) Exercise time

1. Measure your weight on a scale before training without clothes and shoes. (Example: 70 kg or 154 lbs) Weight:                  

During training keep track of fluid consumption and if you make any (3) restroom stops.

(Example: Consumed 32 fl oz of sports drink and 8 fl oz of water during a 120 min run. 40 fl oz total consumed or 1200 ml fluid) 1 fl oz = 30 ml fluid.

2. Amount of fluid consumed:                   fl oz

3. Restroom stops:                           (if any)

  • 16 fl oz ( 480 ml) of fluid weighs about 1 lb

4. Measure weight without clothing or shoes after your training run (69 kg or 151.8 lbs) Weight:            

  • 154 lbs person running for 2 hours and consumed 1200 ml fluid lost 2.2 lbs or 1 kg (lost 1.4% of usual weight)
  • Add the amount of weight lost to the amount of fluid consumed:

5. Running for                       hours

This athlete lost 2.2 lbs and consumed about 2.6 lbs (1200 ml or 40 fl oz) worth of fluid = 4.7 lbs lost or 75 fl oz lost in 2 hours or a sweat rate of 37 fl oz per hour.

You can also use the color of your urine to assess your hydration status.  If you are not urinating every 2-4 hours or your urine is very dark/concentrated, you are most likely dehydrated. Your urine color should be a light yellow color, like lemonade.

In order to hydrate well during the summer or while training make sure to drink water throughout the day and eat plenty of fruits and vegetables which are also a great source of fluids. During your runs, if you are running more than 60 minutes, you may want to consider drinking a sports drink to provide your body with energy (carbohydrates) and electrolytes. Most standard sports drinks provide 50-80 calories/ 8 fl oz and 110-170 mg of sodium.

After your runs make sure to pay attention to your thirst and drink water or a sports drink if you are a “heavy sweater” or notice salt on your clothing. If hours pass and your have not urinated after a run, make sure to drink fluids! If your runs last longer than 60 minutes chocolate milk or a homemade smoothie (8 fl oz of milk or soy milk blended with a banana and frozen berries) can help you hydrate as well as refuel muscles.

Although a beer or an ice cold alcoholic beverage may sound good after a great run, remember that alcohol is a diuretic and can lead to further dehydration. Before enjoying an alcoholic drink, make sure to hydrate adequately with plenty of fluids and eat a balanced meal or snack!

 

By Paula Mrowczynski-Hernandez, RD, LD

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