New research suggests pedaling in the Tour de France gives competitors bigger hearts -- or perhaps it requires those hearts to begin with.
The study's author says virtually all of those who competed in the race have enlarged hearts -- up to 40 percent bigger than average.
So-called "athlete's heart" is a phenomenon long noted by scientists. The heart's walls become thicker to handle the increased blood volume, helping increase oxygen levels and improve endurance.
Dr. Richard Becker says the cyclists are "a special breed."
Becker is a professor of medicine at Duke University and spokesman for the American Heart Association. He's not connected to Carre's study.
"Athlete's heart" is attributed largely to rigorous training. But researchers still aren't sure if they are just larger to begin with.