Runners on a desert trail Runners on a desert trail A new study says heat is a greater threat to runners than originally thought. (Photo: Warren Goldswain / Shutterstock)

Heat stroke more life-threatening for runners than previously thought, study says

Cardiologists at Tel Aviv University made an unexpected discovery while studying athletes.

When a runner goes into cardiac arrest during a race, it’s often headline news – and it’s often diagnosed as a heart condition.

A new study out of Tel Aviv University, however, says the likely culprit is the heat, not the heart. After studying more than 137,000 runners who competed in road races between 2007 and 2013, a team of cardiologists found that heat stroke is 10 times more likely than cardiac events to be life-threatening during endurance races in warm climates.

The study, published in the Journal of the American College of Cardiology, could improve the accuracy of diagnoses for runners who collapse during races. This is especially important as endurance races – events longer than 6.2 miles – gain in popularity. But the key takeaway of the study, the researchers say, is the importance of knowing your body.

Heat stroke is defined as a core body temperature at or above 104-105 degrees and can lead to organ failure. Symptoms can include disorientation, weakness, nausea and vomiting. 

"It's important that clinicians educate runners on the ways to minimize their risk of heat stroke, including allowing 10-14 days to adjust to a warm climate, discouraging running if a person is ill or was recently ill – because a pre-existing fever impairs the body's ability to dissipate additional heat stress – and developing better methods of monitoring body core temperature during physical activity," said Dr. Sami Viskin, one of the authors of the study and a cardiologist at Tel Aviv Medical Center.

Viskin and his team launched their study after noticing the heavy media attention focused on athletes who are stricken during races, specifically those who experience heart attacks. Often an undetected heart condition is revealed only after the athlete has died, which is used to explain the cardiac event.

runner diagnosis

But the team found that those cases are much rarer than they appear. More frequently, they found, runners were collapsing due to heat stroke. During the course of the study, two of the 137,000 runners suffered serious cardiac events later diagnosed as heart-related, and neither were life-threatening. However, 21 of those runners developed heat stroke, 12 were considered life-threatening and two were fatal.

The team's findings go against previous studies, including one published in the New England Journal of Medicine that found one death from heat stroke and 42 from cardiac arrest, and have sparked a debate in the medical community. But despite the polarizing effect of these and other studies, all sides can agree on one thing: heat stroke is a dangerous, and preventable, condition, and there are many ways to avoid it.

Drinking water, for instance, is not an automatic cure for heat stroke. "There's this underlying misconception that if all you do is drink what you lose so that your body stays in balance, then you'll be protected from heat stress," Brent Ruby, director of Montana Center for Work Physiology and Exercise Metabolism, told the Huffington Post. But that's not always the case. What should come first, he said, is knowing your body.

"Heat injuries are 100 percent preventable," Ruby said. "The things that get in the way of heat injuries being preventable are your ego, your coach's ego – just dumb practices, and inexperience."

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