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Exertional heat illness in adolescents and adults: Epidemiology, thermoregulation, risk factors, and diagnosis

Francis G O'Connor, MD, MPH, FACSM
Douglas J Casa, PhD, ATC, FACSM, FNATA
Section Editors
Daniel F Danzl, MD
Karl B Fields, MD
Deputy Editor
Jonathan Grayzel, MD, FAAEM


Exertional heat illness (EHI) is among the leading causes of death in young athletes each year [1,2]. A report by the United States Centers for Disease Control (CDC) found that EHI occurs both during practice and competition and noted a disturbing trend of increasing incidence [3]. Clinicians who care for athletes, both young and old, and others who exert themselves in the heat (eg, firefighters, soldiers, construction workers) need to be aware of the basic physiologic principles of thermoregulation, the spectrum of heat illness, strategies for prevention and treatment, and current guidelines for determining safe return to play or work.

The process of thermoregulation and the epidemiology, clinical presentation, and diagnosis of the different types of exertional heat illness, including exertional heat stroke, are reviewed here. The management of exertional heat stroke and other forms of exertional heat illness is discussed separately, as are exercise-associated hyponatremia, nonexertional heat stroke, malignant hyperthermia and other causes of severe hyperthermia, and heat illness in children. (See "Exertional heat illness in adolescents and adults: Management and prevention" and "Exercise-associated hyponatremia" and "Severe nonexertional hyperthermia (classic heat stroke) in adults" and "Malignant hyperthermia: Clinical diagnosis and management of acute crisis" and "Neuroleptic malignant syndrome" and "Heat stroke in children" and "Heat illness (other than heat stroke) in children".)


Exertional heat illness (EHI) is an ever present danger when athletes, military personnel, or laborers perform intense exercise in the heat. A table summarizing important functional, acquired, and congenital risk factors for EHI is provided (table 1).

Despite great progress educating athletes, coaches, and clinicians, deaths related to exertional heat stroke (EHS), the most severe form of EHI, appear to be on the rise [2]. Deaths from EHS were higher during the period from 2005 to 2009 than any other five year period over the past 35 years. The United States Centers for Disease Control report a weighted average of 9237 cases of EHI among high school athletes per year for the period 2005 to 2009 [3]. The United States military, despite a continued focus on prevention, reported an increase in exertional heat stroke cases (344) in 2014 compared with 2013 [4].

In the United States, the highest incidence of EHS is found among participants in American football, in whom the condition occurs at a rate of 4.5 cases per 100,000 athlete exposures. According to an annual survey of catastrophic American football injuries presented in 2008, 31 players have died from EHS since 1995 [2]. Most cases occurred during summer practice when players are less fit, and temperatures and humidity are often high. According to our data, only one death from EHS occurred among American collegiate football players between 2003 and 2011 during traditional August practices due to the adoption of heat acclimatization policies in 2003. However, problems persist in high school football and collegiate strength and conditioning training, during which a disproportionate number of deaths have occurred [5].


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