Roberts acknowledged that their data didn't take marathon preparation into account. "How do we know how many people we lose with shorter [training] races?" he asked.
He said that with proper conditioning, distance running "is safe if you listen to your body, if you don't try to push through chest pain or shortness of breath, or if you don't ignore factors like very high cholesterol."
"All runners, whether they're young or old, should have a discussion with their doctors about their intent to run and in that discussion there should be a very clear assessment of risk factors," Baggish said.
The Cleveland Clinic offers advice on marathon fitness preparation.
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