ORLANDO, Fla. — Here's a warning for weekend warriors: A new study says swim-bike-run triathlons pose at least twice the risk of sudden death as marathons do.

The research was presented Saturday at a cardiology conference in Orlando, Fla. The study was led by Dr. Kevin Harris, a cardiologist at the Minneapolis Heart Institute at Abbott Northwestern Hospital.

The study found about 15 out of every million triathlon participants die of sudden death, usually from heart problems during the swim event. That's a low risk, but not inconsequential when several hundred thousand Americans participate every year.

Doctors advise having a checkup first to make sure you don't have hidden heart problems.