Jan 29, 2015
Heat Illness Study Roundup

By Abigail Funk

As we head toward preseason practices for football and other fall sports, heat illness is on every athletic trainer’s mind. Here is some of the most recently published heat illness-related research.

It’s impossible to ignore cases like that of Chad Wiley, a senior tackle at North Carolina A&T State University who died in late May following a collapse after a voluntary workout. The initial diagnosis is that Wiley’s death was the cause of heat illness, but the temperature at the time of the workout was only 73 degrees.

According to the Annual Survey of Football Injury Research, Wiley is the 34th football player to die from heat illness complications since 1995. Though the rate of deaths has slowed, they are still occurring every single preseason.

It has long been thought there may be a connection between heat stroke and a genetic mutation that causes malignant hyperthermia. And researchers may now have proved that link does exist through a new study involving mice.

A genetic and protein defect causes malignant hyperthermia in about one in 10,000 patients undergoing general anesthesia. Muscle rigidity and a rapid rise in body temperature result from malignant hyperthermia, but can be treated with a drug called dantrolene that relaxes the muscles.

Researchers studied mice with the same genetic mutation and found that they showed the same symptoms when undergoing anesthesia as when they were exposed to 105-degree Fahrenheit temperatures. Researchers say that establishing the link between heat stress and the genetic mutation that causes malignant hyperthermia has opened doors to further study the connection and a possible cure.

On the football front, a study presented at the 2008 Orthopaedic Society for Sports Medicine Annual Meeting in July examined the effectiveness of forcing cool, dry air between an athlete and his football pads. Results showed a dramatic decrease in core body temperature with this approach.

The study, led by Mary Beth Horodyski, EdD, Associate Professor and Director of Research for the Department of Orthopedics and Rehabilitation at the College of Medicine at the University of Florida, monitored 15 athletes in practice pads for two practice sessions–one with cool air blown under shoulder pads and another with no air circulation between pads.

The day that the researchers used the forced-air approach, the practice session was split into three 15-minute exercise periods, with 10-minute rest periods in between and a 20-minute recovery period at its conclusion. On this day, the athletes had as much as a one-degree Fahrenheit reduction in core body temperature, as well as a heart rate between eight and 10 beats lower than the day without the air application.

After two years of following marathon runners during “hot races,” two researchers were able to show a more direct connection between hot temperatures and marathon runner injuries. Presented at the American College of Sports Medicine (ACSM) Annual Meeting in May, the research documented that almost half of the racers in a 2007 race in Amsterdam were unable to finish, and 20 percent of the runners in a 2006 race in Minnesota needed intravenous fluids after crossing the finish line.

The study recommends canceling marathon races when the temperature hits 82 to 86 degrees, though the researchers admit factors like cloud cover, runners’ acclimatization abilities, and medical services available on-site all impact a cancellation decision. The ACSM official Position Stand says that even in temperatures as low as 65 degrees, runners can be at risk for heat illness.

Finally, the methods athletic trainers and other sports medicine professionals are using to measure core body temperatures are being called into question. A 2007 study led by Douglas J. Casa, PhD, ATC, FACSM, Director of Athletic Training Education at the University of Connecticut, showed that mouth, armpit, air, and temporal probes do not gauge core body temperature as accurately as a rectal thermometer or ingestible thermometer pill.

Another 2007 study looked specifically at the effectiveness of temporal scanning thermometry, and found that it is very ineffective when measuring core body temperature in athletes thought to be under heat stress. The study, published in Medicine & Science in Sports and Exercise last summer, recorded the temperatures of 16 subjects exposed to gradual heat stress over a period of 50 minutes.

Temperatures intestinally derived rose as expected, while those from the temporal probes stayed below pre-heat stress temperatures. The research authors do not recommend using temporal probes when checking core body temperatures in relation to a heat illness, citing the possibility for a poor return-to-play decision.

Abigail Funk is an Assistant Editor at Training & Conditioning.

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