I know it's Science Daily, but:
Dr. Eric Larose reported at the Canadian Cardiovascular Congress in 2010
on a study he'd performed, MRI scans of runners' hearts before and after marathons. What he found was that some hearts showed injury following a marathon, others did not. But the likelihood and degree of injury was correlated with a runner's VO2 max, the maximum amount of oxygen the cardiovascular system can supply. This can be improved with training, but a good portion of it is genetic. Elite cyclists and other athletes could have a VO2 in the 80's or even 90's, while a good club racer might have a VO2 of only 56 ... still much higher than a couch potato. What's unfair is someone like Lance Armstrong could have a VO2 of 56 without training, while the average athlete needs to train like mad to reach that level.
So yes, extreme aerobic running might damage the heart of someone who is not properly conditioned, or genetically disadvantaged. Those are the ones you hear about. Extreme aerobic sports aren't for everyone, but properly done are probably beneficial for most people, if it doesn;t kill you. But so can inactivity.
Clogging of the arteries is another case. It is possible that the 26-year old swimmer's heart wasn't clogged, but that deposits somewhere else broke free and traveled to the heart, blocking its blood supply. No symptoms but sudden death. An aortal aneurism can be undetected and symptomless untill it bursts, as happened to a college baskeball player. A meteor could burst through you roof and kill you in your bed as you slept, or worse while making love. That doesn't make love-making dangerous. Many heart attacks happen while sleeping. Should sleep then be avoided?
Consider the Tarahumara Indians of Mexico, who routinely run ultra-marathons just to get to a neighboring village. They typically live into their 80's and 90's (if they don't die in infancy), still running though maybe a bit more slowly. They do this on a high-carb diet, consisting mostly of corn mash, pine nuts and an occasional mouse or other piece of meat, and lots of beer. Heart disease is unknown. Mayb
e it's generations of breeding, maybe not. Some outsiders have adopted their running lifestyle with some marathoning success. Maybe it's the beer.
Edited by maxwatt, 17 June 2012 - 04:14 AM.