Guidelines for the Prevention of Heat Stroke - Heat Illness
The following measures apply to the prevention of heat illness of all types, but we are primarily concerned with heat stroke since it is clearly the most dangerous form of heat illness.
These recommendations are intended for extreme combinations of exercise and heat, such as military boot camp or pre-season football drills. It is important to adapt these suggestions to particular environmental and exercise conditions faced by the individual. An understanding of the mechanism of heat illness is always indispensible in effective prevention.
1. Medical History and Physical Examination
A complete medical history and physical examination before vigorous training programs are begun is necessary. Factors that increase the risk of heat stress and heat illness must be considered. Athletes who are obese, in poor physical condition, non-acclimatized, exceptionally eager, or who have been recently ill with fever or gastro-intestinal disorders run greater risk of heat illness than others. Previous history of heat illness should be noted.
2. Conditioning
Those in better physical condition have better protection against heat illness than overweight, out-of-shape athletes. Fitness does not confer absolute protection, however, especially in those who are unacclimatized.
3. Acclimatization
Most heat illness occurs during the first few days of strenuous training programs. In addition to the principles of acclima tization examined above, it is clear that training sessions should be light and brief initially, then slowly lengthened and intensified as tolerance increases. Overexertion on the first exposure may lead to disability and the inhibition of acclimatization.
4. Clothing
Clothing should be light and well-ventilated-maximum sweat evaporation is the goal. For football players, short cutoff T-shirts and lightweight shorts are best for early season practice. When full uniforms are worn, white, lightweight, short-sleeved jerseys with shirttails left out are preferred. Clean clothing should be used each day. Headgear should be as light as possible to allow air movement while limiting radiant heat from sunlight.
Excess padding, taping, long stockings, long sleeves, double jerseys, etc., should be avoided. Rubber clothing and sweat suits are of no value and should be eliminated entirely. Sweat suits increase body temperature and fluid loss by hampering heat dissipation. The only possible advantage gained by the use of sweat suits is that they may help acclimatize when used in cool climates. They should not be used in hot climates, for they serve no useful purpose and may be quite dangerous.
These recommendations are intended for extreme combinations of exercise and heat, such as military boot camp or pre-season football drills. It is important to adapt these suggestions to particular environmental and exercise conditions faced by the individual. An understanding of the mechanism of heat illness is always indispensible in effective prevention.
1. Medical History and Physical Examination
A complete medical history and physical examination before vigorous training programs are begun is necessary. Factors that increase the risk of heat stress and heat illness must be considered. Athletes who are obese, in poor physical condition, non-acclimatized, exceptionally eager, or who have been recently ill with fever or gastro-intestinal disorders run greater risk of heat illness than others. Previous history of heat illness should be noted.
2. Conditioning
Those in better physical condition have better protection against heat illness than overweight, out-of-shape athletes. Fitness does not confer absolute protection, however, especially in those who are unacclimatized.
3. Acclimatization
Most heat illness occurs during the first few days of strenuous training programs. In addition to the principles of acclima tization examined above, it is clear that training sessions should be light and brief initially, then slowly lengthened and intensified as tolerance increases. Overexertion on the first exposure may lead to disability and the inhibition of acclimatization.
4. Clothing
Clothing should be light and well-ventilated-maximum sweat evaporation is the goal. For football players, short cutoff T-shirts and lightweight shorts are best for early season practice. When full uniforms are worn, white, lightweight, short-sleeved jerseys with shirttails left out are preferred. Clean clothing should be used each day. Headgear should be as light as possible to allow air movement while limiting radiant heat from sunlight.
Excess padding, taping, long stockings, long sleeves, double jerseys, etc., should be avoided. Rubber clothing and sweat suits are of no value and should be eliminated entirely. Sweat suits increase body temperature and fluid loss by hampering heat dissipation. The only possible advantage gained by the use of sweat suits is that they may help acclimatize when used in cool climates. They should not be used in hot climates, for they serve no useful purpose and may be quite dangerous.
5. Temperature and Humidity
Temperature and humidity measurements should be taken immediately before exercise sessions and every thirty minutes afterward. The WBGT (Wet Bulb Globe Temperature Index) is the most reliable system. The Index is based on the humidity, air temperature, and radiant heat, with greatest emphasis on the former. This three-thermometer device may not be practical because of its expense and required calculations. An inexpensive, simple and effective device is the wet bulb-black globe thermometer. It consists of two thermometers and has a heat index scale printed on it from which a safe level of physical activity can be determined. The sling psychrometer is essentially the same, consisting of the two thermometers and a scale.
Hourly dry and wet bulb readings may be obtained from local weather stations or commercial airports. The wet bulb temperature takes humidity into account. It consists of a thermometer placed in a wet wick. Since more water evaporates at lower humidities, the heat lost as water evaporates will lower the reading on the thermometer. At 100 percent humidity, no heat can be lost by evaporation. The WBGT Index is more complex.
6. Practice Schedules
Initially, exercise sessions should be brief and light. Daily exertion and heat exposure can be progressively increased for the first seven to ten days. Sessions should be no more than 1 ½ to 2 hours long and should not be held during the hottest periods of the day.
(The WBGT peaks at 3 to 4 p.m.) If sessions are longer than. one hour, there should be ten-minute rest periods every thirty minutes. Rest periods should be taken in cool, shaded, breezy areas and clothing loosened to allow ventilation.
Temperature and humidity measurements should be taken immediately before exercise sessions and every thirty minutes afterward. The WBGT (Wet Bulb Globe Temperature Index) is the most reliable system. The Index is based on the humidity, air temperature, and radiant heat, with greatest emphasis on the former. This three-thermometer device may not be practical because of its expense and required calculations. An inexpensive, simple and effective device is the wet bulb-black globe thermometer. It consists of two thermometers and has a heat index scale printed on it from which a safe level of physical activity can be determined. The sling psychrometer is essentially the same, consisting of the two thermometers and a scale.
Hourly dry and wet bulb readings may be obtained from local weather stations or commercial airports. The wet bulb temperature takes humidity into account. It consists of a thermometer placed in a wet wick. Since more water evaporates at lower humidities, the heat lost as water evaporates will lower the reading on the thermometer. At 100 percent humidity, no heat can be lost by evaporation. The WBGT Index is more complex.
6. Practice Schedules
Initially, exercise sessions should be brief and light. Daily exertion and heat exposure can be progressively increased for the first seven to ten days. Sessions should be no more than 1 ½ to 2 hours long and should not be held during the hottest periods of the day.
(The WBGT peaks at 3 to 4 p.m.) If sessions are longer than. one hour, there should be ten-minute rest periods every thirty minutes. Rest periods should be taken in cool, shaded, breezy areas and clothing loosened to allow ventilation.
7. Fluid and Salt Intake
Fluids should be given liberally at rest intervals. Ten ounces of cold water with one to four teaspoons of salt per gallon at rest periods every half hour has been recommended. Smaller quantities at more frequent intervals (four ounces every ten to fifteen minutes) may increase fluid intake. Commercial preparations are good but expensive. The solution should be cool (54 to 59 F). Colder fluid is not harmful, but some individuals may have abdominal discomfort after drinking cold liquids.
During the first few days increasing salt intake is especially crucial. A daily salt supplement of five to fifteen grams daily may be necessary. Generous salting of the food should be encouraged and sometimes is all that is needed. Salt supplements can be decreased in seven to ten days. Virtually all unacclimatized people exerting themselves in the heat will need salt supplements. Salt tablets should be avoided though, since they can irritate the stomach and cause nausea and vomiting, thus worsening dehydration and salt deficiency.
After about three days, the salt content of the solution can be decreased and further diminished with the advent of cooler weather. Acclimatized individuals usually get all the salt they need by salting their food.
8. Weight Charts
Each participant should be weighed before and after exercise sessions. Day-to-day weight loss will consist almost entirely of water losses, and so failure to regain lost weight overnight is a clear sign of dehydration. Weight reduction diets during the acclimatization period should be avoided.
Daily weight loss should not exceed 3 percent of body weight or five pounds. Weight loss in excess of this amount necessitates a curtailment of activity, observation, and an increased fluid intake. A weight loss of more than ten pounds after any workout is dangerous and further activity should not be allowed until rehydration has occurred.
An alternate but less direct method for estimating the adequacy of fluid replacement is that of measuring daily urine. This should be at least 850 cc (about one quart) daily. If the body is dehydrated, the kidneys conserve water by excreting less, thus decreasing the volume of urine.
9. Living Quarters
Cooled or air conditioned living quarters are desirable. This makes rehydration easier, decreases skin disorders, and enhances rest.
10. Education
Athletes and coaches should know the warning signs of heat illness and methods or prevention.
Probably 98 percent of heat strokes are preventable. Each possible contributing factor must be carefully weighed. Coaches, trainers, athletes, and outdoorsmen must be continually aware of the dual menace of heat and humidity.
Fluids should be given liberally at rest intervals. Ten ounces of cold water with one to four teaspoons of salt per gallon at rest periods every half hour has been recommended. Smaller quantities at more frequent intervals (four ounces every ten to fifteen minutes) may increase fluid intake. Commercial preparations are good but expensive. The solution should be cool (54 to 59 F). Colder fluid is not harmful, but some individuals may have abdominal discomfort after drinking cold liquids.
During the first few days increasing salt intake is especially crucial. A daily salt supplement of five to fifteen grams daily may be necessary. Generous salting of the food should be encouraged and sometimes is all that is needed. Salt supplements can be decreased in seven to ten days. Virtually all unacclimatized people exerting themselves in the heat will need salt supplements. Salt tablets should be avoided though, since they can irritate the stomach and cause nausea and vomiting, thus worsening dehydration and salt deficiency.
After about three days, the salt content of the solution can be decreased and further diminished with the advent of cooler weather. Acclimatized individuals usually get all the salt they need by salting their food.
8. Weight Charts
Each participant should be weighed before and after exercise sessions. Day-to-day weight loss will consist almost entirely of water losses, and so failure to regain lost weight overnight is a clear sign of dehydration. Weight reduction diets during the acclimatization period should be avoided.
Daily weight loss should not exceed 3 percent of body weight or five pounds. Weight loss in excess of this amount necessitates a curtailment of activity, observation, and an increased fluid intake. A weight loss of more than ten pounds after any workout is dangerous and further activity should not be allowed until rehydration has occurred.
An alternate but less direct method for estimating the adequacy of fluid replacement is that of measuring daily urine. This should be at least 850 cc (about one quart) daily. If the body is dehydrated, the kidneys conserve water by excreting less, thus decreasing the volume of urine.
9. Living Quarters
Cooled or air conditioned living quarters are desirable. This makes rehydration easier, decreases skin disorders, and enhances rest.
10. Education
Athletes and coaches should know the warning signs of heat illness and methods or prevention.
Probably 98 percent of heat strokes are preventable. Each possible contributing factor must be carefully weighed. Coaches, trainers, athletes, and outdoorsmen must be continually aware of the dual menace of heat and humidity.
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