Football, one of the most popular sports in the United States, is additionally recognized as a leading contributor to sports injury secondary to the contact collision nature of the endeavor. There are an estimated 1.1 million high school football players with another 100,000 participants combined in the National Football League (NFL), college, junior college, Arena Football League, and semipro levels of play.1 USA Football estimates that an additional 3 million youth participate in community football leagues.1 The National Center for Catastrophic Sports Injury Research recently calculated a fatality rate of 0.14 per 100,000 participants in 2014 for the 4.2 million who play football at all levels—and 0.45 per 100,000 in high school.1 While direct deaths from head and spine injury remain a significant contributor to the number of catastrophic injuries, indirect deaths (systemic failure) predominate. Exertional heat stroke (EHS) has emerged as one of the leading indirect causes of death in high school and collegiate football. Boden and colleagues2 reported that high school and college football players sustain approximately 12 fatalities annually, with indirect systemic causes being twice as common as direct blunt trauma.2The most common indirect causes identified included cardiac failure, heat illness, and complications of sickle cell trait (SCT). It was also noted that the risk of SCT, heat-related, and cardiac deaths increased during the second decade of the study, indicating these conditions may require a greater emphasis on diagnosis, treatment, and prevention. This review details for the team physician the unique challenge of exercising in the heat to the football player, and the prevention, diagnosis, management and return-to-play issues pertinent to exertional heat illness (EHI).
The Challenge
EHS represents the most severe manifestation of EHI—a gamut of diseases commonly encountered during the hot summer months when American football season begins. The breadth of EHI includes several important clinical diagnoses: exercise-associated muscle cramps (heat cramps); heat exhaustion with and without syncope; heat injury with evidence of end organ injury (eg, rhabdomyolysis); and EHS. EHS is defined as “a form of hyperthermia associated with a systemic inflammatory response leading to a syndrome of multi-organ dysfunction in which encephalopathy predominates.”3 EHS, if left untreated, or even if clinical treatment is delayed, may result in significant end organ morbidity and/or mortality.
During exercise, the human thermoregulatory system mitigates heat gain by increasing skin blood flow and sweating, causing an increased dissipation of heat to the surrounding environment by leveraging conduction, convection, and evaporation.4,5 Elevated environmental temperatures, increased humidity, and dehydration can impede the body’s ability to dissipate heat at a rate needed to maintain thermoregulation. This imbalance can result in hyperthermia secondary to uncompensated heat stress,5 which in turn can lead to EHI. Football players have unique challenges that make them particularly vulnerable to EHI. The summer heat during early-season participation and the requirement for equipment that covers nearly 60% of body surfaces pose increased risk of volume losses and hyperthermia that trigger the onset of EHI.6 Football athletes’ body compositions and physical size are additional contributing risk factors; the relatively high muscle and fat content increase thermogenicity, which require their bodies to dissipate more heat.7
An estimated 9000 cases of EHI occur annually across all high school sports,8 with an incidence of 1.6:100,000 athlete-exposures.8,9 Studies have demonstrated, however, that EHI occurs in football 11.4 times more often than in all other high school sports combined.10 The incidence of nonfatal EHI in all levels of football is 4.42-5:100,000.8,9 Between 2000 and 2014, 41 football players died from EHS.1 In football, approximately 75% of all EHI events occurred during practices, while only 25% of incidents occurred during games.8
Given these potentially deadly consequences, it is important that football team physicians are not only alert to the early symptoms of heat illness and prepared to intervene to prevent the progression to EHS, but are critical leaders in educating coaches and players in evidence-based EHI prevention practices and policies.
Prevention
EHS is a preventable condition, arguably the most common cause of preventable nontraumatic exertional death in young athletes in the United States. Close attention to mitigating risk factors should begin prior to the onset of preseason practice and continue through the early season, where athletes are at the highest risk of developing heat illness.
Primary Prevention
Primary prevention is fundamental to minimizing the occurrences of EHI. It focuses on the following methods: recognition of inherent risk factors, acclimatization, hydration, and avoidance of inciting substances (including supplements).