Collegiate football players are at the greatest risk of suffering an exertional heat illness within the first 14 days of preseason practices, according to a study published online earlier this month in the Journal of Athletic Training. Seeing as heat illness is “a leading cause of death and disability among U.S. high school athletes,” according to the Centers for Disease Control and Prevention, the study’s findings underscore the importance of a heat-acclimatization period as fall preseason sports practices begin.
To evaluate which circumstances most frequently lead to heat illnesses, the authors collected data from 60 colleges and universities that participated in NCAA Division I or Division III football from 2004 through 2007, recording 114 team seasons over that span.
Across the 365,810 athletic exposures they tracked—defined as every instance of a player participating in a practice or a game—553 cases of exertional heat illness were recorded. Nearly three-fourths of the reported illnesses were exertional heat cramps, while the other 146 were either heat synocope (dizziness accompanied by a brief episode of fainting) or heat exhaustion. The Southeast had an overwhelming majority of the reported cases (446 of 553) and the highest rate of exertional heat illnesses.
The researchers found that the greatest risk of exertional heat illness came during the first three practices and the first three practice days. When two-a-day practices were allowed beginning on the sixth day of practice, they found a higher rate of exertional heat illnesses occurred on the seventh and 10th days of practice. The incidence rate “remained relatively stable” starting on the 14th day of practice.
They also measured how wet bulb globe temperature (WBGT)—which takes into account temperature, humidity, and wind speed—affected the rate of heat illnesses, finding that the incidence rate spiked six-fold when the WGBT was 82 degrees Fahrenheit compared with when it was 76 to 78 degrees Fahrenheit. The severity of heat illnesses also rose with temperatures: The rate of heat syncope/heat exhaustion was 4.12 per 1,000 athlete exposures in “extreme risk” practices (with a WGBT above 90 degrees Fahrenheit) compared with 0.23 in low-risk practices (below 82 degrees Fahrenheit) and 1.34 in moderate-risk (between 82.1 and 86.0 degrees Fahrenheit) and high-risk practices (between 86.1 and 90 degrees Fahrenheit).
“Additional consideration should be given to at-risk individuals, player position, practice day, and practice session at the beginning of the football season and when the WBGT reaches high levels,” the authors conclude. “More practice modifications may be needed to reduce the risk of a catastrophic incident for these individuals.”
Preventing heat illness has long been a focus of youth-sports-safety experts. In 2011, the American Academy of Pediatrics released guidelines for managing student-athletes in extreme heat, recommending a 14-day, graduated return to physical activity in which the intensity and duration progressively increases.
The National Athletic Trainers’ Association issued a similar recommendation in 2014, suggesting student-athletes go through a seven- to 14-day heat-acclimatization period during the preseason to reduce the risk of heat illnesses. For football players specifically, NATA proposed limiting them to no more than three hours of practice wearing only helmets the first two days, no more than three hours of practice wearing only helmets and shoulder pads during the third and fourth days, and no more than three of hours of practice while wearing full athletic equipment on the fifth day.
In 2012, the National Federation of State High School Associations released a free online course for coaches on how to prevent heat illnesses. At the time, the organization said exertional heat stroke was the leading cause of preventable death in high school athletics.
With the risk of exertional heat illnesses reportedly highest within the first few days of practice, the evidence suggests that coaches should familiarize themselves with how to gradually acclimate their athletes to the heat during preseason. Failing to do so could have dire consequences.
A version of this news article first appeared in the Schooled in Sports blog.