Runners must hydrate properly

Apr 27 2005

Seeking to clarify complex issues involving hydration for athletes, the American College of Sports Medicine (ACSM) today reiterated its statements on hyponatremia and dehydration for athletes during endurance events.

Hyponatremia is a dangerous condition that may arise when athletes consume too much water or sports drinks, diluting or disrupting the body's sodium levels. ACSM experts in sports medicine and exercise science point out that while hyponatremia is a serious concern, excessive fluid consumption resulting in hyponatremia is unlikely to occur in most athletes, and hydration is important for all active people. Water and sports drinks, when consumed as recommended, are not dangerous to athletes.

“Runners in Boston this year seem to have gotten the message,” said Larry Kenney, Ph.D., FACSM, referring to the Boston Marathon (April 18.) Kenney is a past president of ACSM and an expert on hydration and related issues. “Despite relatively warm temperatures, this was a race where most participants appeared to be properly hydrated. While hyponatremia has gotten more attention lately, far more athletes are affected by dehydration.”

Dehydration again was the largest concern during the Boston Marathon. According to The Boston Globe, “Late [Monday] afternoon, the main tent, which contained approximately 240 cots, was mostly full of dehydrated runners complaining of nausea, diarrhea, and vomiting.” Hospital officials reported a single case of hyponatremia in this year’s marathon, involving a runner who was released after treatment. Other typical complaints included blisters and cramps. Overall, runners are thought to have suffered about half the medical problems reported in the 2004 race.

Appropriate fluid intake before, during and after exercise is important to help regulate body temperature and replace body fluids lost through sweating. “Runners should follow a hydration plan based on their sweat losses during training, and slow runners in particular should take care not to drink beyond that level during exercise,” said Kenney. He also advised runners to consume salty snacks before and after the race to replace any sodium lost during exercise. ACSM's current hydration guidelines state that those exercising for more than one hour may benefit from sports drinks, which replace carbohydrates for energy.

Generally, says Kenney, persons participating in typical athletic or work environments should continue to heed current hydration guidelines. “There are dangers associated with both extremes of behavior—severe under-drinking and severe over-drinking. Not drinking at all is not a safe option for preventing hyponatremia.” The key, he said, is “drinking intelligently, not drinking maximally.”

Dehydration resulting from the failure to replace fluids during exercise can limit the body's ability to regulate body temperature by sweating and/or skin blood flow, and may contribute to heat exhaustion, heat injury, and exertional heat stroke. To minimize the potential for thermal injury, ACSM experts recommend that athletes attempt to replace fluid losses by consuming fluids at a rate equal to the sweat rate. This can be accomplished by athletes weighing themselves before and after the exercise bout. Recommendations are based on scientific data and observation of athletes suffering from heat injury.

ACSM experts also contend that active people, not just endurance athletes, should be mindful of the need for hydration during activity and exercise in the heat and humidity. Those at risk for dehydration and its consequences, such as hikers, skiers and landscapers, can safely continue their activity following the ACSM guidelines.

ACSM's Position Stand, "Exercise and Fluid Replacement," is the fourth issue of fluid replacement guidelines and recommendations for fluid ingestion and the prevention of heat injury during exercise. Published in Medicine & Science in Sports & Exercise®, it is the product of scientific data and expert consensus on the subject.

The American College of Sports Medicine is the largest sports medicine and exercise science organization in the world. More than 20,000 international, national and regional members are dedicated to advancing and integrating scientific research to provide educational and practical applications of exercise science and sports medicine.