by Mike Broderick
Most runners and active exercisers understand that proper hydration is important for good health and athletic performance. Unfortunately, much of the popular information about hydration which has been commonly accepted over the years has been shown to be inaccurate or even dangerous. Recent research has given us much more accurate information about human fluid needs and better guidelines for maintaining proper hydration and electrolyte balance during exercise. The good news is that the basic information is pretty straightforward and not too hard to follow. In the paragraphs below I will try to summarize the most recent information on fluid and electrolyte replacement for active individuals as documented in the most recent Position Stand on Exercise and Fluid Replacement issued by the American College of Sports Medicine. To obtain a complete copy of the Position Stand, you can go to http://tinyurl.com/2ajwxt and download the .pdf file from the ACSM website.
Proper hydration is essential to good health, and this is particularly true for active individuals engaged in purposeful physical activity such as running and other forms of exercise. The average human body is made up of approximately 60% water, with leaner individuals having up to 75%. Water is needed to maintain blood volume and to help to regulate body temperature through sweat production. In warmer and more humid environments, sweat losses of fluid can be substantial and these can lead to dehydration and decreased athletic performance and health risks, including heat illnesses. Sweating also leads to the loss of important electrolytes, principally sodium and potassium, which are components of sweat and which are important for good health and proper functioning of the neurological and musculoskeletal systems. All persons engaged in exercise should be conscious of and follow good hydration and electrolyte replacement practices.
1. Prehydration: Try to maintain a constant state of good hydration on a daily basis by drinking regularly as dictated by thirst. A general guideline is around 8-12 cups of water a day, plus additional fluid for exercise needs. Try to weigh yourself first thing in the morning most days to establish a "baseline" weight for good fluid balance. If you are generally well hydrated and not in a weight loss mode, your morning nude body weight should not fluctuate by more than about 1%. If it does, this is a good indication that you are dehydrated. Before a significant athletic event or exercise bout, try to consume fluids slowly over a several hour period to allow for fluid absorption and time for urine output to return to normal. Drinking a sports drink with sodium will help stimulate thirst and retention of the consumed fluids. Consuming large quantities of fluid just before an event to "super hydrate" will likely not provide any performance benefit, will surely lead to a great increase in the need to urinate before and during the event and may cause problems with dilution of blood sodium levels and lead to a risk of hyponatremia.
2. During Exercise: Once your event or exercise bout has commenced, the goal is to maintain fluid balance and avoid dehydration by consuming sufficient fluids, along with some carbohydrate and electrolytes during prolonged exercise. A good general guideline is to try to drink about 6-8 ounces of water or sports drink every 15-20 minutes. The best advice is to determine your own individual sweat rate and replace what you lose, rather than trying to follow some published guideline for how much to drink, which may not apply to you. To do this, you simply weigh yourself naked before heading out for a run, and then weigh yourself again naked at the end of the run. Each pound of weight loss from the run is the rough equivalent of 2 cups of water (16 ounces). Of course, you have to account for any fluids you may have consumed during the run itself. So, for example, if you ran for an hour and did not have anything to drink during the run, and upon weighing yourself at the end of the run find that you are 3 pounds lighter than when you started, you know that you need to replace 48 ounces of fluid in that hour (that’s a pretty heavy sweater!). If you are only 1 pound lighter, you only need to replace 16 ounces of water. So-you can see that for some people following the general guidelines for hydration may leave them either severely dehydrated or possibly over hydrated and at risk of hyponatremia. Don’t forget that environmental factors will have a large effect on fluid needs and you may need to modify your intake depending on the temperature and relative humidity.
3. After Exercise: Upon completion of your run or other exercise activity, you should try to fully replace all fluid losses to regain a state of normal hydration. Weighing yourself after a run, and each morning, will help to establish your ongoing needs for fluid replacement. Particularly in warmer weather where sweat losses may have been greater, replacing lost electrolytes by eating some salty snacks or sports drink with added electrolytes is important.
Exercise can cause significant sweating and water and electrolyte losses, particularly in warmer weather. Failure to replace the water and electrolytes lost in sweat will lead to dehydration, which in turn can cause declines in athletic performance and an increased risk of heat illness such as heat exhaustion and heat stroke. Drinking too much fluid can lead to symptomatic exercised induced hyponatremia, a serious medical condition in which blood sodium levels drop too low and which can result in coma, seizure and death. Developing your own individualized fluid replacement program to account for your personal fluid needs is the best way to maintain a good state of healthy hydration. Once you have calculated your own fluid needs, consuming the appropriate amount of fluid during exercise, particularly drinks containing carbohydrates and electrolytes will improve your performance and help to avoid potential health problems. Now that summer is upon us here in Washington, pay attention to your hydration needs and take a water bottle of your favorite sports drink with you when you head out for a run.