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No one ever expects an elite athlete who can swim, cycle, and run multiple miles in one competition could succumb to death in in the prime of life and in the middle of a competition no less. But it happens and, in fact, it did happen this weekend at the New York City's first Ironman triathlon.

A forty-three-year-old athlete from Hong Kong identified in the media as Andy Naylor was pulled from the water near the end of the 2.4-mile swimming section of the competition in the Hudson River.

According to The New York Times, emergency medical staff performed CPR on the man before putting him in an ambulance but these measures did not save him.

The swimming segment of the Triathlon was followed by a 112-mile bide ride on the Palisades Interstate Parkway then a 26.2-mile run ending in Manhattan. Some 2,500 individuals participated in the event. Two other people died last year in the swim portion of the shorter New York City triathlon, also during the swim portion in the Hudson river.

The cause of death in this recent tragedy is unknown and awaits the results of an autopsy. An organizer told The Times that there were 38 lifeguards, as well as kayakers, Coast Guard boats, spectator boats, and Jet Skis stationed along the course as a safety measure.

However, one of the most common problems that can occur in this kind of event is an electrolyte abnormality resulting in a life-threatening heart arrhythmia or abnormal heart rhythm and then sudden cardiac death, says Eugene Storozynsky, M.D., Ph.D., assistant professor of medicine at the University of Rochester Medical Center.

People lose electrolytes when they sweat and must replenish them by drinking fluids. If an athlete does not stay well hydrated before the start of the race, low magnesium or potassium levels might predispose him to heart arrhythmia.

Such a problem "definitely happens but it's also extremely rare," says Dr. Storozynsky.

An athlete "could easily have had some underlying structural heart disease which went unnoticed and, for whatever reason, came to light at the time of the competition," he adds.

A 2010 study in the Journal of the American Medical Association analyzed autopsy reports on nine athletes who had died in triathlons between 2006 and 2008 and found that seven of them had cardiovascular abnormalities.

All told, 14 triathletes died while competing in that span of time, but autopsy reports were not available for five of them.

On the other hand, at this point, it's impossible to know if the athlete who died this weekend had a cardiac problem at all.

"He could have had a stroke. It could have been a very anxiety-provoking event that led to some kind of stress-induced state," says Dr. Storozynsky.

People competing in athletic events need to make sure they stay well hydrated while also being careful not to overintoxicate themselves with water as that can cause electrolyte imbalances as well, Dr. Storozynsky says.

Add juice or milk to the water you're drinking, he recommends.

If you develop any new symptoms such as increased tiredness or uncharacteristic shortness of breath, don't just ignore them. "It would not be unreasonable to get that checked out," Dr. Storozynsky says.

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