National Federation of State High School Associations (NFHS)
Sports Medicine Advisory Committee (SMAC)
DEHYDRATION, ITS EFFECTS ON PERFORMANCE, AND ITS RELATIONSHIP TO HEAT ILLNESS:
- Appropriate hydration before, during, and after physical activity is an important ingredient to healthy and successful sports participation.
- Weight loss during exercise and other physical activity represents primarily a loss of body water. A loss of just 1 to 2% of body weight (1.5 to 3 pounds for a 150-pound athlete) can negatively impact performance. A loss of 3% or more of body weight can significantly increase the risk for exertional heat-related illness. If an athlete is already dehydrated prior to beginning activity, these effects will occur even sooner.
- Athletes should be weighed (in shorts and T-shirt) before and after warm or hot weather practice sessions and contests to assess their hydration status.
- Athletes with high body fat percentages can become significantly dehydrated and over-heat faster than athletes with lower body fat percentages while working out under the same environmental conditions.
- Athletes have different sweating rates and some lose much more salt through their sweat than others. “Salty sweaters” will often have noticeable salt stains on clothing after workouts, and often have a higher risk of developing exertional muscle cramps.
- Poor heat acclimatization/fitness levels can greatly contribute to an athlete’s heat intolerance and heat illness risk.
- Certain medications, or fever, can negatively affect an athlete’s hydration status and temperature regulation, increasing the risk for heat illness.
- Environmental temperature and humidity each independently contribute to dehydration and heat illness risk.
- Clothing that is dark or bulky, as well as protective equipment (such as helmets, shoulder pads, and other padding and coverings), can increase body temperature, sweat loss and subsequent dehydration and heat illness risk.
- Even naturally dry climates can have high humidity on the field if irrigation systems are scheduled to run prior to early morning practices start. This temporary increase in humidity will continue until the water completely soaks into the ground or evaporates.
- A heat index chart should be followed to help determine if practices/contests should be modified or canceled. The NOAA National Weather Service’s heat index chart can be found at: http://www.weather.gov/om/heat/index.shtml
- On-site wet-bulb temperature should be measured 10-15 minutes before practices or contests. The results should be used with a heat index to determine if practices or contests should be started, modified, or stopped.
- If wet-bulb temperature measurement is not available, the heat index for your approximate location can be determined by entering your postal zip code: http://www.osaa.org/heatindex/
Example of the effects of relative humidity on the risk for dehydration and heat illness:
- A relative humidity of 40 percent and a temperature of 95 degrees Fahrenheit are associated with a likely risk of incurring heat illness if strenuous physical activity is conducted. However, even with a lower air temperature of only 85 degrees Fahrenheit, the risk for exertional heat illness could be the same or greater with a higher relative humidity of 70 percent.
WHAT TO DRINK DURING EXERCISE AND OTHER PHYSICAL ACTIVITY:
- For most exercising athletes, water is appropriate and sufficient for pre-hydration and rehydration. Water is quickly absorbed, well-tolerated, an excellent thirst quencher and cost-effective.
- Traditional sports drinks with an appropriate carbohydrate and sodium formulation may provide additional benefit in the following general situations:
- Prolonged continuous or intermittent activity of greater than 45 minutes
- Intense, continuous or repeated exertion
- Warm-to-hot and humid conditions
- Traditional sports drinks with an appropriate carbohydrate and sodium formulation may provide additional benefit for the following individual conditions:
- Poor hydration prior to participation
- A high sweat rate or “salty sweater”
- Poor caloric intake prior to participation
- Poor acclimatization to heat and humidity
- A 6 to 8% carbohydrate formulation is the maximum that should be utilized in a sports drink. Any greater concentration will slow stomach emptying and potentially cause the athlete to feel bloated. An appropriate sodium concentration (0.4–1.2 grams per liter) will help with fluid retention and distribution and decrease the risk of exertional muscle cramping.
WHAT NOT TO DRINK DURING EXERCISE:
- Fruit juices with greater than 8 percent carbohydrate content and carbonated soda can both result in a bloated feeling and abdominal cramping.
- Athletes should be aware that nutritional supplements are not limited to pills and powders as many of the new “energy” drinks contain stimulants such as caffeine and/or ephedrine.
- These stimulants may increase the risk of heat illness and/or heart problems with exercise. They can also cause anxiety, jitteriness, nausea, and upset stomach or diarrhea.
- Many of these drinks are being produced by traditional water, soft drink and sports drink companies which can cause confusion in the sports community. As is true with other forms of supplements, these "power drinks”, “energy drinks”, or “fluid supplements" are not regulated by the FDA. Thus, the purity and accuracy of contents on the label is not guaranteed.
- Many of these beverages which claim to increase power, energy, and endurance, among other claims, may have additional ingredients that are not listed. Such ingredients may be harmful and may be banned by governing bodies like the NCAA, USOC, or individual state athletic associations.
- See the NFHS Position Statement and Recommendations for the use of Energy Drinks by Young Athletes for further information.
HYDRATION TIPS AND FLUID GUIDELINES:
- Many athletes do not voluntarily drink enough water to prevent significant dehydration during physical activity.
- Drink regularly throughout all physical activities. An athlete cannot always rely on his or her sense of thirst to sufficiently maintain proper hydration.
- Drink before, during, and after practices and games. For example:
- Drink 16 ounces of fluid 2 hours before physical activity.
- Drink another 8 to 16 ounces 15 minutes before physical activity.
- During physical activity, drink 4 to 8 ounces of fluid every 15 to 20 minutes (some athletes who sweat considerably can safely tolerate up to 48 ounces per hour).
- After physical activity, drink 16 to 20 ounces of fluid for every pound lost during physical activity to achieve normal hydration status before the next practice or competition.
- The volume and color of your urine is an excellent way of determining if you’re well hydrated. Small amounts of dark urine means that you need to drink more, while a “regular” amount of light-colored or nearly clear urine generally means you are well-hydrated. A Urine Color Chart can be accessed at: http://at.uwa.edu/admin/UM/urinecolorchart.doc
- Hyponatremia is a rare, but potentially deadly disorder resulting from the over consumption of water. It is most commonly seen during endurance events, such as marathons, when participants consume large amounts of water over several hours, far exceeding fluid lost through sweating. The opposite of dehydration, hyponatremia is a condition where the sodium content of the blood is diluted to dangerous levels. Affected individuals may exhibit disorientation, altered mental status, headache, lethargy, and seizures. The diagnosis can only be made by testing blood sodium levels. Suspected hyponatremia is a medical emergency and EMS (Emergency Medical Services) must be activated. It is treated by administering intravenous fluids containing high levels of sodium.
Casa DJ, Armstrong LE, Hillman SK, et al. National Athletic Trainers’ Association position statement: Fluid replacement for athletes. Journal of Athletic Training 2000;35:212-224.
McKeag DB, Moeller JL. ACSM’s Primary Care Sports Medicine. 2nd Ed, Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins, 2007.
Montain SJ. Hydration recommendations for sport 2008. Current Sports Medicine Reports 2008;7:187-92.
National Collegiate Athletic Association. Guideline 2c: Prevention of heat illness. 2010-11 Sports Medicine Handbook (21st edition).
Sawka MN, Burke LM, Eichner ER, et al. American College of Sports Medicine position stand. Exercise and fluid replacement. Medicine & Science in Sports & Exercise 2007;39:377-90.
Revised and Approved October 2011
DISCLAIMER – NFHS Position Statements and Guidelines
The NFHS regularly distributes position statements and guidelines to promote public awareness of certain health and safety-related issues. Such information is neither exhaustive nor necessarily applicable to all circumstances or individuals, and is no substitute for consultation with appropriate health-care professionals. Statutes, codes or environmental conditions may be relevant. NFHS position statements or guidelines should be considered in conjunction with other pertinent materials when taking action or planning care. The NFHS reserves the right to rescind or modify any such document at any time.