I.      The National Weather Bureau, on its radio station, broadcasts an hourly heat index reading.  It is strongly recommended that all schools use this service to make judgments about athletic contests.  Basically, precautionary measures should be taken when the heat index is between 95 and 105 degrees.  Over 105 degree heat index indicates a significant danger level.

        A.   The following procedures should be followed for athletic contests scheduled during the day in hot weather:

                1.     The National Weather Service, that is broadcast every hour, should be checked at 1:00 p.m. on the day before a game, as well as one hour before the scheduled start of the contest.

                2.     If heat index is stated between 95 and 105 degrees, plans should be implemented to alter game conditions for both schools.

                3.     If heat index is stated over 105 degrees, plans to postpone or reschedule   athletic contest should be implemented (both schools).

        B.  The following procedures should be followed for athletic contests scheduled during           the evening in hot weather:

                1.     The National Weather Service, that is broadcast every hour, should be checked three (3) hours before schedule contest.

                2.     If a heat index between 95 and 105 degrees is stated, plans should be implemented to alter game conditions that day (both schools).

                3.     If a heat index over 105 degrees is stated, plans to postpone or reschedule athletic contest should be implemented (both schools).

        C.  The following procedures should be considered for practice sessions when a dangerous heat index level is indicated:

                1.     Possible cancellation of all practice.

                2.     Shorter practice time.

                3.     Early morning or late evening practice.

                4.     Move outside practice sessions indoors.


II.     A combination thermometer may be obtained at most hardware stores.  These can be used and kept on the fields to indicate wet bulb globe readings.  A radio weather cube is obtainable at most radio shops.  This can be kept in the Athletic Office and as mentioned, hourly heat index readings are available.  Also, weather alerts are given when indicated.


III.    It is recommended that a weight chart be kept for each individual athlete and posted in the locker room or available area.  Each athlete should weigh in at the beginning of each practice session and weigh out at the end of each practice session.  The percentage of weight loss should be calculated.  A weight loss greater than three (3) percent should indicate potential danger of excessive loss of body fluids during the practice sessions and accordingly, adequate fluid replacement should be maintained throughout the remainder of that day.  Greater than five (5) percent weight loss indicates the possibility and significant danger of developing a heat-related illness.


IV.   It must be instilled in the athletes by the coaches that water and salt replenishment is a continual process and not a "stop-gap maneuver."  Athletes should be encouraged during hot weather to drink adequate quantities of fluid throughout the day at home, as well as at practice sessions.  During practice sessions, water should be available to them at all times.  Obviously, the hotter, more humid weather indicates more frequent water breaks.  This can be scheduled either up to every ten (10) to fifteen (15) minutes during extremes or if applicable, free water intake should be allowed during the entire practice session.  Salt replacement is also a daily process and the athletes should be encouraged to adequately salt their foods during all meals.  It is not advised to use salt tablets at any time.  These can actually cause more danger, as they cause more concentrations in the stomach and can lead to nausea, vomiting and stomach problems.  Salted solutions may be given during practice sessions but certainly water is adequate.


V.    It is recommended that practice sessions during middle and late August be scheduled as much as possible during the early morning hours and late evening hours.  For example, 8 o'clock practice in the morning and 6:00 p.m. practices seem to be advisable.

        When more than one practice session per day is encountered, sufficient recovery time should be observed between sessions.


VI.   It is recommended that during hot weather in game situations several heat breaks be called in addition to any other time-outs.  It is recommended that at least three (3) breaks per quarter be done by the officiating crew.  (For Football).


VII.  Heat disorders may be classified as heat cramps, heat syncope, heat exhaustion and heat stroke.

        **     These Guidelines were adopted by the St. Louis Suburban Athletic Conference for their member schools effective 1985-86 school year with the cooperation of Dr. Charles Mannis and Dr. Benji Boonshaft.  The guidelines have been edited by the MSHSAA.


Heat Stress and Athletic Participation

Frederick O. Mueller, Ph.D.


Early fall football, cross country, soccer and field hockey practice are conducted in very hot and humid weather in many parts of the United States.  Due to the equipment and uniform needed in football, most of the heat problems have been associated with football.  Under such conditions the athlete is subject to:

Heat Cramps -- Painful cramps involving abdominal muscles and extremities caused by intense, prolonged exercise in the heat and depletion of salt and water due to profuse sweating.

Heat Syncope -- Weakness, fatigue and fainting due to loss of salt and water in sweat and exercise in the heat.  Predisposes to heat stroke.

Heat Exhaustion (Water Depletion) -- Excessive weight loss, reduced sweating, elevated skin and core body temperature, excessive thirst, weakness, headache, and sometimes unconsciousness.

Heat Exhaustion (Salt Depletion) -- Exhaustion, nausea, vomiting, muscle cramps, and dizziness due to profuse sweating and inadequate replacement of body salts.

Heat Stroke -- An acute medical emergency related to thermoregulatory failure.  Associated with nausea, seizures, disorientation, and possible unconsciousness or coma.  It may occur suddenly without being preceded by any other clinical signs.  The individual is usually unconscious with a high body temperature and a hot dry skin (heat stroke victims, contrary to popular belief, may sweat profusely).


It is believed that the above mentioned heat stress problems can be controlled provided certain precautions are taken.  According to the American Academy of Pediatrics Committee on Sports Medicine, heat related illnesses are all preventable.  (Sports Medicine: Health Care for Young Athletes, American Academy of Pediatrics, July 2000).  The following practices and precautions

are recommended:

        1.   Each athlete should have a physical examination with a medical history when first entering a program and an annual health history update.  History of previous heat illness and type of training activities before organized practice begins should be included.  State high school associations recommendations should be followed.

        2.   It is clear that top physical performance can only be achieved by an athlete who is in top physical condition.  Lack of physical fitness impairs the performance of an athlete who participates in high temperatures.  Coaches should know the PHYSICAL CONDITION of their athletes and set practice schedules accordingly.

        3.   Along with physical conditioning the factor of acclimatization to heat is important.  Acclimatization is the process of becoming adjusted to heat and it is essential to provide for GRADUAL ACCLIMATION TO HOT WEATHER.  It is necessary for an athlete to exercise in the heat if he/she is to become acclimatized to it.  It is suggested that a graduated physical conditioning program be used and that 80% acclimatization can be expected to occur after the first 7-10 days.  Final stages of acclimatization to heat are marked by increased sweating and reduced salt concentration in the sweat.

        4.   The old idea that water should be withheld from athletes during workouts has NO SCIENTIFIC FOUNDATION.  The most important safeguard to the health of the athlete is the replacement of water.  Water must be on the field and readily available to the athlete at all times.  It is recommended that a minimum 10-minute water break be scheduled for every half hour of heavy exercise in the heat.  Athletes should rest in a shaded area during the break.  WATER SHOULD BE AVAILABLE IN UNLIMITED QUANTITIES. 

        5.   Check and be sure athletes are drinking the water.  Replacement by thirst alone is inadequate.  Test the air prior to practice or game using a wet bulb, glove, temperature index (WBGT index) which is based on the combined effects of air temperature, relative humidity, radiant heat and air movement.  The following precautions are recommended when using the WBGT Index:  (ACSM's Guidelines for the Team Physician, 1991)

                Below 64 - Unlimited activity

                65-72 - Moderate risk

                74-82 - High risk

                82 Plus - Very high risk


         6.  There is also a weather guide for activities that last 30 minutes or more (Fox and Matthew, 1981) which involves knowing the relative humidity and air temperature:

                  AIR TEMP                  DANGER ZONE             CRITICAL ZONE

                  70 F                            80% RH                          100% RH

                  75 F                            70% RH                          100% RH

                  80 F                            50% RH                          80% RH

                  85 F                            40% RH                          68% RH

                  90 F                            30% RH                          55% RH

                  95 F                            20% RH                          40% RH

                  100 F                         10% RH                          30% RH

                  RH = RELATIVE HUMIDITY


                One other method of measuring the relative humidity is the use of a sling psychrometer, which measures wet bulb temperature.  The wet bulb temperature should be measured prior to practice and the intensity and duration of practice adjusted accordingly.  Recommendations are as follows:

                Under 60 F - Safe but always observe athletes

                61-65 F - Observe players carefully

                66-70 F - Caution

                71-75 F - Shorter practice sessions and more frequent water and rest breaks

                75+ F - Danger level and extreme caution


         7.  Cooling by evaporation is proportional to the area of skin exposed.  In extremely hot and humid weather reduce the amount of clothing covering the body as much as possible.  NEVER USE RUBBERIZED CLOTHING.

        8.   Athletes should weigh each day before and after practice and WEIGHT CHARTS CHECKED.  Generally a 3-percent weight loss through sweating is safe and over a 3-percent weight loss is in the danger zone.  Over a 3-percent weight loss the athlete should not be allowed to practice in hot and humid conditions.  Observe the athletes closely under all conditions.  Do not allow athletes to practice until they have adequately replaced their weight.

        9.   Observe athletes carefully for signs of trouble, particularly athletes who lose significant weight and the eager athlete who constantly competes at his/her capacity.  Some trouble  signs are nausea, incoherence, fatigue, weakness, vomiting, cramps, weak rapid pulse, visual disturbance and unsteadiness.

        10.  Teams that encounter hot weather during the season, through travel or following an unseasonably cool period, should be physically fit but will not be environmentally fit. Coaches in this situation should follow the above recommendations and substitute more frequently during games.

        11.  Know what to do in case of such an emergency and have your emergency plans written with copies to all your staff.  Be familiar with immediate first aid practice and prearranged procedures for obtaining medical care, including ambulance service.


Heat Stroke:  THIS IS A MEDICAL EMERGENCY-DELAY COULD BE FATAL.  Immediately cool body while waiting transfer to a hospital.  Remove clothing and place ice bags on the neck, in the axilla (armpit), and on the groyn areas.  Fan athlete and spray with cold water to enhance evaporation.


Heat Exhaustion:  OBTAIN MEDICAL CARE AT ONCE.  Cool body as you would for heat stroke while waiting for transfer to a hospital.  Give fluids if athlete is able to swallow and is conscious.


Summary:  The main problem associated with exercising in hot weather is water loss through sweating.  Water loss is best replaced by allowing the athlete unrestricted access to water.  Water breaks two or three times every hour are better than one break an hour.  Probably the best method is to have water available at all times and to allow the athlete to drink water whenever he/she needs it.  Never restrict the amount of water an athlete drinks, and be sure the athletes are drinking the water.  The small amount of salt lost in sweat is adequately replaced by salting food at meals.  Talk to your medical personnel concerning emergency treatment plans.