As warmer weather and the road racing season begins, I am frequently asked about dehydration and the best hydration strategies for runners.
How important is proper hydration for runners? Dehydration as little as 2% of body weight can begin to significantly impact performance. For an athlete that has a higher sweat rate (greater than 2 liter per hour), that level of dehydration can occur after 30 minutes of exercise in hot and humid conditions. Additional, research has shown that level of dehydration can slow 10-km run times by 6.3% compared to running in a hydrated state. That equates to a race time almost 3 minutes slower if you usually run a 40-minute 10k!
Tips
Calculate your fluid losses – An easy way to determine sweat rate and fluid losses is to weigh yourself before and after a run, but before rehydrating. A one-pound weight loss is roughly equal to 500 ml (about 1 pint) of fluid loss. Remember to account for any fluids you drank during the workout.
Match your fluid losses – Overhydration can be as problematic as dehydration. If you overhydrate, you run the risk of hyponatremia. Since there is a wide variety in the rate of fluid loss among individual runners, the current American College of Sports Medicine guidelines don’t recommend a specific volume of fluid to drink per hour. A better guide to fluid replacement is to drink when thirsty and attempt to at least partially replace fluid loss during exercise.
Pre-hydrate – Starting a race or a training run already slightly dehydrated can have an impact on performance. Make sure you start a workout or a race well hydrated and start hydrating at least 60 minutes before exercise if possible. Smaller amounts of fluids (200 to 500 ml) are more easily and quickly absorbed -For longer races such as marathons, there may be a slight risk of developing mild hyponatremia (low blood sodium) before the race. Liquids containing electrolytes may decrease this risk compared to hydrating with only with water.
Drink during the run – Get in the habit of drinking during longer runs. Try running with a water bottle or run a course that has water or other fluids available. If you don’t like running with a water bottle, try a shorter loop course and leave the fluids at the start. Take a short break each time you pass the starting point.
Set the timer on your watch for every 15 or 20 minutes to remind yourself to drink. Try a sports drink for runs lasting longer than 60 minutes to help replace sodium and carbohydrates.
Post Work-out – Rehydration after exercise is also important for recovery. The best strategies include drinking smaller amounts of fluid over a period of time instead of drinking a large amount quickly once you finish the run. Sports drinks with electrolytes including sodium may help you to rehydrate quicker compared to water. A post-race meal higher in sodium will also help stimulate the urge to drink and replace lost fluids.
John M. Martinez, M.D. is Medical Director of Coastal Sports & Wellness Medical Center in San Diego, a comprehensive sports medicine clinic focusing upon active patients and athletes. Find out more at www.coastalsportsmedicine.com
This article originally appearred as part of the May Running Centers email newsletter. To learn more about the Running Centers or to find a location in Southern California, click here.
Posted by John 
