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Exertional Heat Illness Rate Highest In High School Football, Study Finds

Most injuries in August, after more than 2 hours of practice

There is good news and bad news in a new study (3) on exertional heat illness in high school sports: the bad news is that the rate for football players is 11 times higher that of all other sports combined, and that, in a third of the cases, no medical professional was on site at the time of injury. The good news is that, despite a rash of heat-related deaths (6 in 2011 alone, all in football), the overall rate of EHI across all high school sports is low and dropping. 

Football players with tackling dummy

Researchers from a number of universities, including Marshall, the University of North Carolina at Chapel Hill, and the Korey Stringer Institute at the University of Connecticut, found that exertional heat illnesses were widely distributed geographically, not just in hot or humid areas, that most occurred in August, during practice (more than a third more than 2 hours into the practice session), most often in football, and, in a third of the cases, with no medical professional onsite at the time of onset of the illness.

Overall rates

Examining data for the period 2005 to 2011 obtained from the National HIgh School Sports-Related Injury Surveillance System, High School RIO®, the study reported that: 

  • The EHI rate was 1.45 per 100,000 athletic exposures
  • An estimated 51,943 EHI events occurred nationally in the nine original sports studied
  • EHI represented less than 1% (0.6%) of all reported injuries and adverse health events over the period studied (2005/2006-2010/2011 academic years)
  • 75.2% of EHI events occurred during practice, 23.6% during competition. 
  • The EHI rate has decreased over the last 6 years.


Football poses far and away the highest risk of exertional heat illness: 

  • the highest EHI rates (per 100,000 athletic exposures) were reported, not surprisingly, in four warm-weather states: Florida (21.60), Alabama (17.92), Arizona (13.63), and Kentucky (13.08).
  • Among football players, EHI occurred most frequently among offensive lineman (35.7%), defensive linemen (16.9%); and linebackers (9.7%);
  • More than one-third (35.7%) of football players sustaining EHI were offensive linemen, even though they comprised only 18.0% of football players sustaining all other injuries and adverse health events. 
The new study "really reinforces how vulnerable football players are to heat-related illnesses, said University of Georgia climatolgist Andrew Grundstein, interviewed for a April 28, 2013 article in Scientific American (8).

Other sports

  • The next-largest numbers of EHI events occurred in girls' volleyball (4.8%), girl's soccer (3.0%) and boys' wrestling (3.0%)
  • No EHI events were reported in boys' ice hockey, boys' volleyball, girls' softball, girls' gymnastics, or girls' track and field.  
  • The highest EHI rates for all sports combined except for football were Alabama (3.03), Florida (1.49), and New Hampshire (1.35).

Time of year

  • The majority of EHI events occurred in August (60.3%), and, among these, most occurred during the pre-season (90.4%)

Level of play, gender

  • The majority of EHI events involved varsity athletes (58.9%), followed by junior varsity (19.3%) and freshman (12.2%) athletes
  • The proportion of EHI events among all reported injuries and adverse health events was higher for boys than for girls overall, but excluding football, EHI were essentially split evenly among boys and girls; among gender-comparable sports (i.e. soccer, basketball, lacrosse, swimming and diving), the proportion of EHI events did not differ for girls versus boys.

Availability of Medical Professionals

  • Athletic trainers reported that all but one of the EHI events were assessed by at least one sports medicine professional, with a third (33.2%) assessed by two or more.
  • Most EHI events were assessed by athletic trainers (89.1%), followed by physicians (35.1%), and emergency medial technicians (4.3%). 
  • In only two-thirds of EHI events (66.4%) was a medical professional onsite at the start of an EHI event, with athletic trainers constituting the vast majority (95%) of all medical professionals onsite.

Exposure type

  • Of the EHI events reported during practice, 32.0% occurred more than 2 hours into the practice session, but this number was skewed by the proportion of EHI events that occurred more than 2 hours into the practice session in football (36.7%), which was 2.4 times that in all other sports.  

Body Mass Index 

  • More than a third (37.1%) of student-athletes who sustained EHI were obese, a third were normal weight (33.4%) and slightly less than a third (27.4%) were overweight.
  • Among student-athletes sustaining all other injuries and adverse health events, only one in seven (15.5% were obese and one in five (22.%) were overweight. 
  • Within football, BMI was a factor in the onset of EHI: the proportion of football players sustaining EHI who were obese (47.1%) was 1.7 times the proportion of football players sustaining other injuries and adverse health events that were obese (27.5%).


The study recommended:

  • More education: While all schools in the study had an athletic trainer, one AT cannot be present at all sports practices and competitions for one school.  "Therefore, education of sports administrators, coaches, athletes, and parents about the prevention, identification, and management of EHI is critically important," said lead author, Zachary Y. Kerr, MPH, of the Department of Epidemiology at Marshall University.
  • Comply with pre-season heat-acclimatization guidelines: Because a large proportion of the EHI events occured during practice, particularly 2 hours after practice sessions began, adhering to pre-season acclimatization guidelines (8) limiting practice sessions to 2 hours and providing frequent water breaks is recommended.  While a growing number of states, including Georgia, Florida, and Arizona, have adopted all seven of the recommendations of the Korey Stringer Institute and the NATA, states have been slow to act, with only nine meeting all the guidelines as of May 2013. Of the states with the highest EHI rates, Kentucky meets only one; Alabama, none.  [For a handout with the guidelines to give to coaches and other parents, click here]
  • Modify, postpone, or cancel practices if Wet Bulb Globe Temperature too high.  Coaches and athletic trainers should be prepared to modify, postpone, or cancel practices and competitions in accordance with published EHI prevention guidelines using the Wet Bulb Globe Temperature, which combines ambient temperature and ambient humidity into one overall index. 
  • Improved surveillance: strategies are needed to improve surveillance of exertional heat illness in sports  in order to identify risk factors and prevention strategies.

Exertional heat stroke statistics

According to the National Center for Catastrohic Sport Injury Research (1), 35 high school football players died from exertional heat stroke between 1995 and 2010.  In the summer of 2011, six high school players died due to high temperatures and lack of rehydration (2). Indeed, in the 5-year period from 2005 to 2009, more exertional heat stroke deaths occurred in organized sports than in any other 5-year perod over the past 35 years. (2)

  • the majority of sports-related, heat-related deaths in U.S. children and adolescents occur during participation in football, wrestling, and cross-country track (3,4,5)
  • an estimated 9,000 high school athletes are treated for exertional heat illness (EHI) annually, principally during August, at the beginning of the Fall sports season, when athletes are not yet acclimated to physical exertion in the heat (3,6)
  • The estimated incidence rate for nonfatal EHI for high school sports is 1.6 per 100,000 athletic exposures (defined as one athlete participating in one athletic practice or competition)(6), with the highest rates in football (6,7)

1. Mueller F, Colgate B. Annual survey of football injury research, 1931-2010.  National Center for Catastrophic Sports Injury Research: University of North Carolina at Chapel Hill, 2011. www.unc.edu/depts/nccsi/2010fbannual.pdf.

2. Brady E. Heat-related illness still deadly problem for athletes. USA Today, August 15, 2011. www.usatoday.com/sports/2011-08-15-heatstroke-still-causing-death-in-athletes_n.htm. 

3. Kerr ZY, Casa DJ, Marshall SW,Comstock RD. Epidemiology of Exertional Heat Illness Among U.S. High School Athletes. Am J Prev Med 2013;44(1):8 -14) 

4. Mueller FO, Colgate B. Annual survey of football injury research, 1931-2008. National Center for Catastrophic Sports Injury Research, University of North Carolina at Chapel Hill, 2009. www.unc.edu/depts/nccsi/footballannual.pdf. 

5. Mueller FO, Cantu RC. Catastrophic sports injury research: twentyeighth annual report: fall 1982-spring 2010. National Center for Catastrophic Sports Injury Research, University of North Carolina at Chapel Hill. 2010. www.unc.edu/depts/nccsi/2010allsport.pdf. 

6. Yard EE, Gilchrist J, Haileyesus T, et al. Heat illness among high school athletes-U.S., 2005-2009. J Safety Res 2010;41(6):471- 4. 

7. Huffman EA, Yard EE, Fields SK, Collins CL, Comstock RD. Epidemiology of rare injuries and conditions among U.S. high school athletes during the 2005-2006 and 2006-2007 school years. J Athl Train 2008;43(6):624 -30. 

8. Brett Israel and The Daily Climate. "More States Blow Whistle on High School Football Heat Illness." Scientific American; April 28, 2013 

Posted May 2, 2013, Revised and updated February 1, 2017