VHSL Heat Guidelines
HEAT INJURIES CAUSE MULTIPLE DEATHS EACH YEAR IN HIGH SCHOOL SPORTS.
Heat illness and injury can range from a simple muscle cramp to life threatening heat stroke. Catastrophic heat
injuries are preventable. Following the recommendations found in this document, the risk of heat injuries can be
reduced significantly. The most important components in preventing heat injury are the prevention of dehydration
and limiting activity when temperature and humidity make it near impossible for the body to cool through
evaporation of sweat.
The body produces heat at rest, this heat production increases 10 to 20 times with exercise. Evaporation is the major
method of cooling the body during exercise. Evaporation of sweat dissipates the heat from the core of the body,
keeping the internal organs cool. Exercising in a dehydrated state reduces the ability to sweat, therefore
compromising the ability to cool. Dehydration also causes a reduction in blood volume, compromising cardiac
output. The air temperature and humidity have a direct effect on the efficiency of this cooling process. Based on the
effects of dehydration and exercising in the heat and humidity, the following guidelines have been established to
provide administrators, coaches, and athletic training staff, with a sound plan to prevent heat injury.
It is strongly recommended that each school system develops and adheres to specific heat guidelines appropriate for
their student activity population and facilities based on scientific research. Guidelines should also apply to
activities such as marching band and for gyms and indoor facilities without air conditioning.
Signs and Symptoms of Heat Problems:
The following are common signs and symptoms related to heat illness, but are not intended to represent a complete
list. In the event an athlete is suffering from one or more of the following, the athlete should be referred to
appropriate allied health care or medical professional for full evaluation.
• Muscle spasms/cramps
• Heavy or profuse sweating
• Skin is flushed or cool and pale
• Rapid pulse, nausea, weakness
• Disoriented, confusion
• Elevated body core temperature
• Cessation of sweating
• Red, dry skin
• Shallow breathing and rapid pulse
• Loss of consciousness
Heat Illness/Injury Facts:
• Adolescents take longer to acclimatize to the heat than adults
• Weight loss of water greater than 3% of body weight significantly increases the risk of heat related illness.
• 1.5 times the amount of water lost must be consumed to replace lost weight.
• Unrelated illnesses causing vomiting and/or diarrhea will increase risk of heat related illnesses. These
conditions should be brought to the attention of the ATC and/or coaching staff prior to participation and close
monitoring of these individuals should take place during practice sessions and competition.
• Athletes taking certain medications including diuretics, antihistamines, beta blockers and anti-cholinergics are
at higher risk for heat illnesses.
• Light colored breathable clothing can assist the body in cooling.
• Athletes who are overweight, poorly conditioned, recovering from illness, lacking in sleep, or taking
medications are at added risk for heat illnesses and should be monitored closely and/or have their participation
Recommendations for Fluid Replacement:
• All schools should establish a Fluid Replacement Protocol for their facility. (see recommendations below)
• All athletes should inform their coaches and/or athletic training staff of any pre-existing heat illness, gastrointestinal
condition and/or medical complication prior to exercising in the heat.
• Weigh athletes before and after each practice during hot weather. Athletes should conform to a restricted
activity schedule if not within 1% of the previous days PRE-EXERCISE weight.
• Replace fluids at a rate of 24 fluid ounces for every pound of body weight lost after exercise
• Athletes should be educated in the process of hydrating themselves as a 24 hour a day process.
• Athletes should begin every athletic activity well hydrated.
• During exercise, the average person should drink 8 – 12 oz of fluid every 20 to 30 minutes.
• Urine color is an easy method to determine hydration status. Light yellow to clear urine indicates a well-hydrated
• Water should be available to athletes at all times and never be withheld from exercising individuals.
Ambient air temperature and humidity have a direct effect on the ability for a body to cool itself through
the evaporation of sweat. When the air temperature is above 90, and/or the relative humidity is high, the body is at a
higher risk to not effectively stay cool, which may be compounded by the level of dehydration of the body’s fluids.
The following chart is a simple method to determine the amount of increased risk with variations of heat and
humidity, and subsequent suggestions to modify participation in physical activities.
This chart can be used by inputting the temperature and humidity available via local radio stations, Internet
locations, etc. Simply cross-reference the relative humidity (top row) with the temperature (first column) to
determine the humiture. Follow guidelines outlined below.
HUMITURE VHSL RECOMMENDATION
105? and up: Recommend no outside activities.
95? to 104?: Recommend no equipment (helmets, pads, etc) be used during activity.
90? to 94?: Recommend equipment be removed as often as possible (during rest breaks, on sideline,
etc). Careful monitoring of all athletes for signs of heat problems.
Below 89?: Recommend adequate water supply at all practices and competitions with breaks every 20
to 30 minutes for rehydration.
National Athletic Trainers Association’s Recommendations on Fluid Replacement:
• Educate athletes on the effects of dehydration on physical performance.
• Inform athletes on how to monitor hydration status.
• Convince athletes to participate in their own hydration protocols based on sweat rate, drinking preferences, and
personal responses to different fluid quantities.
• Encourage coaches to mandate rehydration during practices and competitions, just as they require other drills
and conditioning activities.
• Have a scale accessible to assist athletes in monitoring weight before, during, and after activity.
• Provide the optimal oral rehydration solution (water, CHOs, electrolytes) before, during, and after exercise.
• Implement the hydration protocol during all practices and games, and adapt it as needed.
• Finally, encourage event scheduling and rule modifications to minimize the risks associated with exercise in the
Journal of Athletic Training Vol. 35 N2, June 2000
Full text can be found on NATA’s website: www.nata.org
Acclimatization to Heat:
Another way to help prevent heat stress is to become acclimatized to the weather. Acclimatization means becoming
adapted to the weather or climate. The process takes 7 to 12 days. Studies have shown adolescents take longer to
acclimatize to heat than adults. As a result of acclimatization, the sweating mechanism of a person is enhanced:
• onset of perspiration occurs earlier
• perspiration increases
• increase in blood volume with the more training an individual does
• improves supply of oxygen to the muscles
• heart rate decreases
• core body temperature does not rise as high during exercise
Other facts about heat illnesses and exercising in the heat:
• Dehydration of 1% to 2% of body weight begins to impact athletic performance
• Dehydration greater than 3% of body weight may increase an athlete’s risk of heat illness.
• Sports drinks should contain less than 8% carbohydrate. Carbohydrate content greater than 8% compromises
the rate of gastric emptying and should be avoided.
• Wear light weight and light colored clothing
• Avoid wearing articles that prevent water absorption
• Early morning commonly produces a humid environment and lower temperatures. Usually, as the sun rises, the
temperature will increase and the humidity decreases. As the evening hours approach, the temperature
decreases and the humidity will rise. Often, the most critical times to monitor athletes ability to exercise in hot
weather occurs when the temperature rises quickly during the early morning prior to the sun burning off the
humidity, or during storms when the humidity remains high due to cloud cover, etc.
• A mild breeze can reduce the humidity on a particular field, as well as improve the evaporative process.
• Field watering after practice sessions are complete can help reduce the ambient humidity on or near an athletic
field, thus reducing the heat stress on athletes.
Alternative methods of assessing adverse heat conditions
EXTRACURRICULAR ACTIVITY DURING
EXTREME HOT AND HUMID WEATHER POLICY
USING WET BULB THERMOMETER
WET BULB TEMPERATURE RECOMMENDATIONS
Courtesy of Fairfax County Public Schools
It should be noted that wet bulb readings represent the temperature including the effect of evaporative cooling. These readings
are more commonly acquired using a sling psychrometer or digital psychrometer available through medical suppliers for under
$100. The use of these devices allows for more accurate monitoring of actual conditions found at an athletic facility.
Fluid replacement should be at a rate of 24 oz for every pound of body weight lost after exercise.
• Light colored, loose clothing is suggested during activity in hot weather.
• Athletes are encouraged to wear sunscreen on exposed skin during hot, sunny conditions.
• Adequate fluid supply should be readily available at all times during activity in hot weather.
• Individuals poorly acclimatized, or poorly conditioned are at increased risk for heat related illness/injury and
should be monitored closely or placed on a modified participation schedule.
• Athletes having a pre-existing dehydrated state (recent fever or gastro-intestinal illness) or pre-existing heat
injury are at a much higher risk for heat related illness/injury and should be monitored closely or placed on a
modified participation schedule.
• Medications including diuretics, antihistamines, beta blockers and anti-cholinergics increase the risk of heat
• Overweight athletes are at increased risk for heat illness/injury and should be monitored closely.
• Energy, ergogenic, and dietary supplements such as Creatine may cause an increase in dehydration and heat
related illness and/or injury.