Extreme weather and environmental conditions can negatively affect athletic performance and, if ignored, can lead to adverse health consequences.
Hyperthermia means Increased body temperature — overheating of the body due to excessive exposure to high heat and humidity. Humidity is the amount of moisture in the air. High temps (80+ degrees ) and high humidity (75+%) can cause heat stress.
The body must be able to dissipate heat. Body temperature and the gain or loss of body heat can be affected by 5 factors.
- Metabolic Heat Production – the heat your metabolism produces and eliminates
- Conductive Heat Exchange – heat transferred between objects of different temperatures that are in direct contact with each other.
- Convective Heat Exchange – heat transferred from a warmer object to a cooler object through air or liquid. If the air is hotter than the skin temperature, then body temperature increases. Likewise, submersion in a cold pool reduces body temperature.
- Radiant Heat Exchange – the body gains heat from the sun as it radiates to the body. Alternately, if you are in the shade, your body emits some of its heat back to the environment.
- Evaporation – body heat loss through sweat evaporation accounts for 20% of overall heat loss. For the body to cool, air must be cooler than the body. At 65% humidity, evaporation slows; at 75% humidity, evaporation stops. Air evaporates sweat and cools the body. 65% of body heat is lost through the head and neck. If the body is dehydrated, it cannot dissipate heat with sweat and become overheated. Devices such as the “cool suits” or “cool vests” worn under pads and hooked into a sideline cooling unit operate under the principle that increased evaporation of sweat serves to cool the body more rapidly. The Cool Zone sideline fans seen at many sporting events emit a cool mist to perform essentially the same function via fast-moving cool moist air.
Monitoring The Heat Index
Monitoring the combination of heat, humidity and sunshine can help to identify those environmental conditions that are likely to lead to hyperthermia. Simply looking at a thermometer is not the best gauge for determining when to curtail outdoor activity. Rather, the Wet Bulb Globe Temperature (W.B.G.T.) is an objective measurement to determine and recommend a safe level of outdoor activity, and when to recommend fluid replacement and rest periods during activity. The drier the air, the greater the evaporation. Conversely, the more humid the air, the less the evaporation. As stated above, reduced evaporation can lead to heat illness.
The W.B.G.T. is determined by the formula:
W.B.G.T. = 0.1 X DBT + 0.7 X WBT + 0.2 X GT
DBT = Dry Bulb Temperature (actual air temperature)
measured with a standard mercury thermometer or psychrometer (see Figure X).
WBT = Wet Bulb Temperature – measured by means of a wet wick or gauze wrapped around the end of a thermometer (hence “wet bulb”) swung around in the air, or by means of a device called a psychrometer.
If the surrounding air is dry, more moisture evaporates from the wick, cooling the wet-bulb thermometer more, producing a greater difference between the readings of the two thermometers. If the relative humidity is 100% – the two thermometers will read the same.
- Psychrometer – While digital psychrometers can be purchased for less than $200, it is possible to create a simple sling psychrometer by attaching two large tube thermometers side by side on a narrow board. Attach a short piece of chain or a handle to the top of the board to permit swinging the device in an overhead circular movement. Then tightly wrap the bulb of one thermometer with a piece of gauze, and wet the end. The newer digital units measure in 90 seconds, but a sling psychrometer may be more accurate.
GT = Globe Temperature – the measurement of the sun’s radiation by means of a black metal case around the end of the thermometer.
To calculate humidity only, measure the difference between the DBT and the WBT.
Dehydration and Fluid Replacement
- thirst (if you are thirsty, you are already slightly dehydrated)
- dry mouth
Sweating — when you sweat you lose electrolytes (sodium, chloride, potassium). Even a 2% (3 pounds in a 150-pound person) loss of body weight due to sweat during exercise can impair performance, and increase the chance of heat illness. If your sweat tastes salty or burns your eyes, you are losing sodium and it must be replaced.
Hydrate 2-3 hours before, during and after activity with a sports drink that contains electrolytes (sodium, chloride, potassium). Gatorade has a good balance of electrolytes and sugar. It contains the optimal carbohydrate level (6% glucose solution =14 grams of sugar per 8 ounces of water) for quick absorption. Studies show that a sports drink is beneficial during both endurance and short-term, high-intensity activities.
The increased sodium allows the body to retain fluid longer than water alone. Drinking water alone turns on the kidneys prematurely and increases the need to urinate. Sports drinks and/or water should be consumed cold (50 degrees) because cold fluids absorb faster and decrease core temperature.
A person should not return to activity until his/her body weight has returned to normal and urine concentration is light in color.
Heat-related illnesses increase when the air temperature and humidity are high and the sun is bright. A fitness professional should be able to differentiate between cramps, syncope (fainting), exhaustion and stroke.
A mild form of heat illness characterized by collapse or fainting. It occurs when blood vessels dilate or blood pools in the legs or arms.
- rapid fatigue
- standing in the heat
- not acclimated to the heat
Another mild form of heat illness
Signs: painful muscle cramps usually in arms, legs, or abdomen
- prolonged sweating = loss of water and electrolytes (sodium, chloride, potassium, magnesium, and calcium)
- not acclimated to the heat
- increase water and electrolyte intake, especially sodium
- approximation of muscle. If that does not work, use direct compression of muscle. If approximation and compression do not work, use reciprocal inhibition innervation (isometrically contract the opposite muscle group)
- ice massage — do not manually massage the area
- rest in a cool area. Often unable to return to activity the same day, as heat cramps are likely to reoccur
A moderate form of heat illness due to environmental heat and exercise; categorized as mild hyperthermia. Most signs of heat exhaustion can be recognized and acted upon before the condition becomes more serious.
- dry tongue and mouth
- profuse sweating
- mental dullness
- loss of coordination
- stomach and/or muscle cramps
- nausea or vomiting
- a headache
- pale skin
- rectal (core) temperature less than 104 degrees. Rectal temperature is the most effective method for
- differentiating between heat exhaustion and heat stroke.
- rapid pulse
- a small amount of urine produced
- not drinking enough water/fluid
- prolonged sweating
- poor physical conditioning
- replace fluids
- administer intravenous fluids
- place person in a cool environment
- apply sponge with cool water, especially to the head and neck
- take rectal temperature
A severe form of heat illness. This is a serious life-threatening emergency that may lead to brain damage or death. Many signs of impending heat stroke present prior to the actual occurrence of heat stroke.
- a headache
- cessation of sweating (occurs in roughly 25% of heat stroke cases)
- confusion or irrational behavior
- sudden collapse with loss of consciousness
- flushed hot skin
- rapid, strong pulse (160-180 bpm)
- rectal temperature of 104 degrees or higher (107 degrees = death)
- increased/shallow respirations
- typically blood pressure doesn’t change
Causes: Unknown, but the condition is defined as a breakdown of the thermoregulatory mechanism caused by an excessively high core temperature
- must decrease body temperature within 45 minutes
- get to an emergency room
- place in a cool location
- immerse in an ice bath, or sponge with ice water and fan; keep an inflatable kids pool on sidelines.
- Decreasing body temperature is more important than water replacement.
Preventing Heat Illness
Fluids should be easily accessible before, during and after activity. Drink 7-10 ounces of cold water and/or a 6% glucose sports drink every 15 minutes to match sweat loss.
A 2% loss of body weight impairs cardiorespiratory and thermoregulatory systems and is categorized as mild dehydration. Too much water decreases sodium levels which compromises the central nervous system and can cause hyponatremia.
Progress training to acclimate to hot weather and used to exercise. A person can expect to achieve 80% acclimatization in 5-6 days, with 2 hours of activity in the morning and 2 hours in the afternoon. 100% acclimatization will take 10-14 days. Most heat-related illnesses occur during the first few days of training. Fitness professionals must take routine temperature and humidity readings. Provide adequate rest periods in a cool, shaded area.
Identifying Susceptible Individuals
People typically more susceptible to heat illness include:
- those with greater muscle mass
- overweight individuals
- those with poor fitness levels
- excessive sweaters
- people that don’t dissipate heat well (including carriers of Sickle Cell Anemia)
- those with a history of heat illness
- those with a poor diet
- people with an infection, fever, gastrointestinal condition, or diarrhea
- those on certain medications
Learn more about recognizing and treating heat-related illnesses and emergencies, as well as other sport-related injuries in the Sports Injury Specialist program.