Even the most highly conditioned athletes need to take special precautions when exercising in hot weather. Athletes are especially prone to heat illness in the summer months, so recognizing signs of heat illness is critical.
The National Athletic Trainers’ Association (NATA) defines five heat illnesses in its 2002 position statement on the topic: exercise-associated (heat) muscle cramps; heat syncope (dizziness); exercise (heat) exhaustion; exertional heat stroke; and exertional hyponatraemia, and lists the signs or symptoms associated with each condition. These are reproduced here as Table 1.
Table 1: Signs and Symptoms of Exertional Heat Illnesses
|Exercise-associated (Heat) Muscle Cramps
||Dehydration, thirst, sweating, transient muscle cramps, fatigue
|Heat Syncope (Dizziness)
||Dehydration, fatigue, tunnel vision, pale or sweaty skin, decreased pulse rate, light headedness, fainting
|Exercise (Heat) Exhaustion
||Normal or elevated core temperature, dehydration, dizziness light-headedness, syncope, headache, nausea,
anorexia, diarrhea, decreased urine output, persistent muscle cramps, pallor, profuse sweating, chills, cool,
clammy skin, intestinal cramps, urge to defecate, weakness, hyperventilation
|Exertional (Heat) Stroke
|High core temperature (>40C), central nervous system changes, dizziness, drowsiness, irrational behavior,
emotional instability, confusion, irritability, hysteria, apathy, aggressiveness, delirium, disorientation,
staggering, seizures, loss of consciousness, coma, dehydration, weakness, hot and wet or dry skin,
tachycardia (100-120bpm), hypotension, hyperventilation, vomiting, diarrhea
||Core temperature <40C, nausea, vomiting, extremity (hands and feet) swelling, low blood sodium level,
progressive headache, confusion, significant mental compromise, lethargy, altered consciousness, apathy,
pulmonary oedema, cerebral oedema, seizures, coma
The traditional approach in sports medicine has been to group heat illnesses as mild, moderate or severe. In this simple classification approach, exercise associated muscle (heat) cramps and heat syncope would fall into the mild category, with heat exhaustion in the moderate category. Exertional heat stroke and hyponatraemia would be in the severe category.
Similarly, the American College of Sports Medicine (ACSM) recently reworked its position stand on exertional heat illness during training and competition and redefined its definitions of heat illnesses accordingly, based upon the now extensive body of research published in this field. Of interest to the fitness professional is the fact that the understanding of how well established illnesses like exertional heat stroke (EHS) and heat exhaustion develop is incomplete. According to the ACSM, “Some athletes tolerate hot conditions, dehydration and hyperthermia well and are seemingly unaffected, while others discontinue activity in relatively less stressful conditions.”
Recognizing and Managing Heat Illnesses
The signs and symptoms of heat illnesses are listed in Table 1 above. Note that it is not necessary for an individual to have all of the symptoms listed for a condition. Rather, the presence of any of these, taking into account the climatic conditions and the exercise load being undertaken, should raise the index of suspicion.
Exertional Heat Stroke
Since exertional heatstroke is a medical emergency, the ACSM position stand rightly focuses on this illness. “EHS is defined by hyperthermia (>40C) associated with central nervous system disturbances and multiple organ system failure,” says the ACSM and “almost all EHS patients exhibit sweat-soaked and pale skin at the time of collapse, as opposed to the dry, hot and flushed skin that is described in the presentation of non-exertion-related ("classic") heatstroke.”
The ACSM notes that predisposing factors to EHS include strenuous exercise in a hot and/or humid environment, a lack of prior acclimatization and poor physical fitness, while noting that “even highly trained and heat acclimatized athletes develop EHS while exercising at high intensity if heat dissipation is inadequate.”
Other conditions also increase the risk of EHS, including obesity, dehydration, sleep deprivation, sunburn, viral illness and diarrhea. “Immediate recognition of EHS cases is paramount to survival,” states the ACSM. Because the signs and symptoms are many and varied and often non-specific, initially the ACSM takes a very simplistic approach, arguing that “any change of personality or performance should trigger an assessment for EHS, especially in hot-humid conditions.”
According to McDermott et al, “only trained medical personnel should assess and treat an athlete with suspected EHS.” However, McDermott et al argue that the fitness professional or strength and conditioning coach should have a working knowledge of EHS and a written emergency action plan.
According to NATA, this is “a relatively rare condition, defined as a serum sodium level less than 130mmol/L”. It would appear that low sodium levels occur when physical activity exceeds four hours. It may be seen when an individual ingests far more water than his body is losing through sweat during exercise or if an athlete’s sodium losses are not adequately replaced. As with EHS, this is a medical emergency, and correct diagnosis and treatment are essential.
Exertional Heat Exhaustion
Heat exhaustion is the most common heat-related disorder seen in active populations, according to the ACSM, who define this as “the inability to continue to exercise,” often with heavy sweating and dehydration. It is seen most frequently in hot, humid conditions. Athletes with suspected heat exhaustion need to be moved to a shady or air conditioned area, have excess clothing removed and placed lying down with legs raised and medical help sought.
Exercise-associated Muscle (Heat) Cramps
Quite simply, these are painful, involuntary muscle contractions during or after intense or prolonged exercise in the heat. Fluid deficiencies and electrolyte imbalances are thought to be the main causes. These cramps seem to be best prevented by maintaining fluid and salt balance.
According to NATA, “heat syncope or orthostatic dizziness can occur when a person is exposed to high environmental temperatures. This condition is attributed to peripheral vasodilatation, postural pooling of blood, diminished venous return, dehydration, reduction in cardiac output and cerebral oedema.” As with heat exhaustion, immediate treatment involves moving the individual to a shaded or air conditioned space and elevating the legs while medical or first aid help is sought.
Preventing Exertional Heat Illness
Clearly, if physical activity is to take place in a hot and humid environment, fitness professionals will be conscious of the increased risk of exertional heat illness and will modify the training session as appropriate. With athletic competition, where activity modification is not possible, acclimatization should be considered. Note that the ACSM in its literature review on the topic states that “10 to 14 days of exercise training in the heat will improve heat acclimatization and reduce the risk of EHS.”
Most obviously, monitoring and tracking hydration status is essential. NATA recommends that athletic trainers ask four key questions in this respect:
- Do I know the pre-exercise weight of the athletes (especially those at high risk) with whom I work, particularly during hot and humid conditions?
- Are the athletes familiar with how to assess urine color and is a urine color chart accessible?
- Do the athletes know their sweat rates and therefore how much to drink during exercise?
- Is a refractometer or urine color chart present to provide additional information regarding hydration status in high risk athletes when baseline bodyweights are checked?
Other non-environmental factors that can be checked are: an individual’s recent illness history (especially viral or involving vomiting and/or diarrhea), the wearing of non-permeable/evaporative clothing and previous day lifestyle behaviors (alcohol intake, medications/drug use).
The top tips for fitness professionals to know when it comes to heat illnesses includes the following:
- Five main heat illnesses have been identified: exercise-associated muscle (heat) cramps; heat syncope; exercise (heat) exhaustion; exertional heat stroke; and exertional hyponatremia.
- Exertional heat stroke (EHS) and exertional hyponatraemia are medical emergencies.
- Predisposing factors to EHS include strenuous or prolonged exercise in a hot humid environment, a lack of prior acclimatization and poor physical fitness.
- Obesity, dehydration, sleep deprivation, sunburn, viral illness and diarrhea also increase the risk of EHS.
- The immediate recognition of EHS is paramount to survival.
- All fitness professionals are recommended to have a working knowledge of heat illnesses and a written emergency action plan.
- Monitoring and tracking hydration status is essential to help avoid heat illnesses.
- Binkley HM et al, National Athletic Trainers’ Association Position Statement: Exertional Heat Illnesses, J Ath Training, 37 (3), pp 329-343, 2002.
- Sherry E and Wilson SF, Oxford Handbook of Sports Medicine, OUP, pp90-91, 1998
- Armstrong LE et al, ACSM Position Stand: Exertional Heat Illness during Training and Competition, Med Sci Sports Exerc 39: 556-572, 2007.
- McDermott BP et al, Exertional Heat Stroke Basics: what strength and conditioning coaches need to know, Strength & Conditioning Journal, 30 (3), pp29-32, 2008.
- Armstrong LE (editor), Exertional Heat Illnesses, Human Kinetics, 2003.