As a former distance runner, it is a brutal sport and no one can convince me it is not unhealthy in the long run. There is growing debate on if heavy cardio is actually putting too much stress and miles on the ticker. They don't have unlimited mileage, and like a car engine, can wear out with overuse. As for shitting yourself, yes nasty. But people eat Chipotle and PF Changs on purpose and do the same thing.