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Many factors, ranging from genetics to inexperience with hot weather, can cause the kind of heat-related illnesses that downed two Jaguars players this week.
But new national guidelines aim to keep athletes safer in the heat, said Larry Kenney, president of the American College of Sports Medicine.
The most important message is for teams to keep a tub and a cooler of ice on hand -- as the Jaguars do -- to quickly immerse overheated players, said Douglas Casa, director of athletic training education at the University of Connecticut who helped write the guidelines, issued in June through the National Athletic Trainers' Association.
"That's a pretty easy and a cheap way to guarantee survival," Casa said.
Jaguars defensive tackle John Henderson collapsed at yesterday morning's practice. Defensive tackle Larry Smith collapsed Sunday.
Casa thinks heat illnesses will never be totally eliminated in professional sports because athletes are competing for high-paying jobs.
"They're going to work their butts off and they're going to overheat," he said.
But Kenney said he considers Jaguars head trainer Mike Ryan one of the most savvy trainers on heat issues, noting Ryan helped develop the new consensus statement on preventing heat illness in athletes, approved by 18 medical, sports and government groups.
"So the fact the Jaguars are experiencing problems says more to football in the NFL and the tremendous heat stresses put on players than to a lack of preparedness," Kenney said.
A prior bout with heat illness will make a player more susceptible to overheating episodes. But otherwise, predicting who might get a heat illness is difficult.
One of the best predictors is the temperature during the previous day's practice, Casa said.
"If it's hot, it weakens them and they can't handle as much the next day," he said.
Both of the Jaguars collapsed in the morning, which isn't unusual, Casa said.
"We see this all the time. The highest-risk time is the second, third and fourth day [of camp]. They're not replacing the fluids they're losing."
Big people have more trouble replacing the fluid they sweat out. Football players commonly lose five to six pounds of fluid an hour.
"The bigger you are, the more heat you produce and the more you'll sweat," Casa said.
Genetics seems to be a factor as well, said Kenney, a professor of physiology and kinesiology at Pennsylvania State University who specializes in heat stress and dehydration.
"If you put 100 people in the same conditions and their body temperature goes up the same amount, some will get sick and some won't," Kenney said.
Lack of acclimatization is another factor. Some athletes from cooler climates aren't used to exercising outside in hot weather. Their bodies need time to adjust to the heat by outputting less sodium in their perspiration and by starting to sweat earlier in the workout.
"That's why most episodes occur in the first two or three days of a football training camp or a military boot camp," Kenney said. "Once you get past the first week of training camp you almost never have heat-related problems."
Athletes need to start gradually exercising outdoors before they ever report to training camp so their bodies can adjust, said Pete Indelicato, team physician for the University of Florida Gators.
And athletes -- or anyone else who works in the heat -- must be diligent about keeping themselves hydrated before, during and after exerting themselves. The effects of dehydration can progressively worsen over time.
"This is an issue you need to pay attention to 24 hours a day, not just a half an hour before" practice, he said.
Drinking water alone isn't enough. Essential electrolytes -- substances such as sodium and chloride -- are lost through perspiration and need replacing. It's important to drink a sports drink or water with salt to replace those electrolytes, he said.
Three heat illnesses in professional athletes are heat cramps, heat exhaustion and heatstroke.
Heat cramps happen when the body lacks enough water to flush lactic acid and other byproducts from muscle cells.
Heat exhaustion occurs when the body produces much more heat than it's able to lose. This causes fatigue and a drop in blood pressure which can result in collapse. But an athlete should start to improve shortly after resting and cooling down, Casa said.
Heatstroke occurs when the body heats to a temperature of 106 degrees or higher. It can damage the brain and other organs and cause death.
In a normal year, about 175 Americans die from heat illness, according to the Federal Emergency Management Agency.
Twenty-one football players have died from heat-related illness since 1995, representing a sharp increase after a decline of several years, according to Frederick O. Mueller, a researcher at the University of North Carolina.
But immersing a player in an ice bath within minutes of overheating will quickly reduce his body temperature, Casa said. Organ damage and death become more likely the longer a person's temperature stays above 106 degrees Fahrenheit, he said.
Kenney noted the NCAA is changing its guidelines for college football to force schools to slowly acclimate players to hot weather. Players will wear only a helmet for the first two days of practice, and one session will last no more than three hours. Players won't wear full uniforms until the fifth day of practice.
The problem is football uniforms hold in heat.
"Once you put in a football uniform you really increase the amount of heat stress on a player," Kenney said.
The NCAA also decided multiple practices won't be allowed on consecutive days, and three hours should be allowed for recovery between sessions.
But none of those rules exists in the NFL.
"In the NFL, time is money," Kenney said. "These guys are out there competing for jobs, trying to impress coaches. It's really a recipe for heatstroke or heat exhaustion."
Kenney said the NFL made one positive move in the past year by banning ephedra. The over-the-counter supplement increases metabolism, which in turn increases body temperature.
Staff writer Marcia Mattson can be reached at (904) 359-4073 or at mmattson@jacksonville.com.
HITTING HOME
For more information about new guidelines to prevent heat illness in athletes, go to Jacksonville.com, keywords: heat illness.
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