Runners Education: Proper Hydration

This is another installation in a series of runners education articles written by UW Health Sports Medicine staff.

Hydration plans are a significant part of the training process for distance events. While a number of factors can affect hydration, runners can and should begin to normalize their routines for hydration to prepare for race day.

Hydration Strategies

Hydration strategies have changed over time. For a time, runners were advised to drink fluids frequently and not allow thirst to set in. This practice led to problems with overhydration and the onset of severe and sometimes life-threatening conditions. So what is a runner to do? If insufficient fluids can lead to one set of problems and too many fluids can lead to a different set of health problems, how do runners decide how much to drink?

The International Marathon Medical Directors Association (IMMDA) suggests returning to the body's physiological roots. Trust your body and drink when it tells you that you need fluid. In short, drink fluids when you are thirsty. At the initial onset of thirst you are well within the boundaries of peak performance levels. Your running times will remain optimal if you are consuming fluids near the onset of thirst.

Estimating Your Hydration Needs

Use a systemic approach to formulate a running hydration plan. And remember that during running electrolytes are lost, as well as fluids. The consumption of sports drinks, fruit and possibly gel for events lasting greater than one hour should be incorporated into your plan.

1. Weigh yourself nude immediately before a run.
2. Run at pace for one hour, keeping track of how much fluid you drink. (Other amounts of time can be used. Simply adjust the formula below to accommodate the change in time).
3. After the run, undress, towel yourself off so that you are dry, and weigh yourself again.
4. Subtract your after-run weight from your pre-run weight and convert this number into ounces. One pound equals 16 ounces. Take this number and add the weight of fluid you drank during the run.
5. Divide that total by four to estimate your fluid loss rate for every 15 minutes. This will provide you an estimate on how much fluid you may need to drink every 15 minutes during your run.

Here's an example. A runner weighs 188 pounds before his run. He consumes 16 ounces of fluid during an hour run, and weighs 187 pounds after the run. So he lost one pound during the run. One pound plus 16 ounces of fluid consumed equals 32 ounces, which is the rate of fluid lost per hour. That divided by four is eight, which is the number of ounces of fluid he should consume for every 15 minutes of running.

This estimate may vary depending on the weather conditions, running conditions (hills versus flat terrain) and choice of clothing. Simulate race conditions as closely as possible for the most accurate estimate.

Best Practice

Remember that the best practice as indicated by the IMMDA for hydration during extended running events is to consume fluids when you are thirsty. The method provided above is to help you plan your estimated hydration needs for race day.

Everyone has different fluid and caloric demands during long-distance running events, so be sure to practice your hydration and calorie intake plan. Have a running plan and practice it, adjust it as needed during your training runs, and prepare yourself to have the best day of running on race day.

Happy training!