It's a phenomenon that astounds even the experts -- a seemingly healthy person dying soon after or during a workout.
And two recent deaths -- Clemson University general counsel Clayton Steadman and former University of South Carolina President Andrew Sorensen -- have put a spotlight on the issue.
Steadman, 56, died April 17. He'd suffered a heart attack three days earlier after working out at a gym, according to Clemson officials.
Sorensen, 72 and a longtime cyclist, died the same day after a bicycle ride in Ohio, where he was fundraising for Ohio State University, according to USC President Harris Pastides.
The cause of their deaths wasn't disclosed.
And while they may have some people thinking, "That could be me," medical experts say that shouldn't keep people from exercising.
"This idea that having a heart attack or dying as a result of exercising is a little counterintuitive," said Dr. Jesse Jorgensen of Carolina Cardiology, speaking generally about the phenomenon.
"We know that regular, habitual exercise is associated with significantly reduced risk of death. But it turns out that in people who don't have physical activity regularly and then go out and exercise, the risk of a cardiac event is increased. Like the weekend warrior."
Sudden cardiac death in men and women who exercise regularly is "pretty uncommon," he said, noting their risk is reduced about 30 percent across the board.
The risk is highest in those who rarely or never exercise -- about three to five times higher for those who only exercise sporadically, according to a new study, he said.
Dr. Michael Payne of Upstate Cardiology agrees that sudden cardiac death after a workout is "pretty infrequent."
"Even though the risk of sudden death is slightly higher during or after exercise," he said, "in an active person who does exercise regularly, the risk is lower."
Neither the American College of Cardiology nor the American Heart Association have data on the number of people who die after exercising.
But in a new study in AHA's journal Circulation, researchers report that at least among NCAA student-athletes, sudden cardiac death is the leading medical cause of death during exercise and that the risk is underestimated.
About one in 44,000 NCAA athletes suffers sudden cardiac death every year, according to the researchers, who examined deaths from January 2004 to December 2008. About 400,000 students participate in NCAA sports each year, they said.
The risk was higher for African-Americans and for males. While basketball had the highest risk with a rate of one in 11,394, the risk in Division I male basketball players was about one in 3,000, the researchers said. Swimming had the second-highest risk, followed by lacrosse, football and cross-country.
According to the Heart Association, athletics can increase the risk in people with underlying heart disease, including the most common cause -- hypertrophic cardiomyopathy, an abnormal growth of heart muscle.
But among the general population, Jorgensen said studies show the average age for sudden cardiac death associated with exercise is around 60 and three quarters of victims are men. It's not clear whether that's because men tend to develop heart problems about 10 years earlier than women or because they do more strenuous activity when they aren't in shape, he said.
Jorgensen recommends that everyone get 30 minutes of regular aerobic exercise five days a week. Neophytes should start out slowly and gradually build up intensity and duration, he said.