From the article...

"The medical director of the London Marathon, Professor Sanjay Sharma, agreed that more research was needed and said the results provided "food for thought".

"My personal feeling is that extreme endurance exercise probably does cause damage to the heart in some athletes. I don't believe that the human body is designed to exercise for as long as 11 hours a day, so damage to the heart is not implausible."

But he said it was too early to say that taking part in endurance sports causes long-term damage."

There has been lots of evidence over the years regarding the damaging effects of extreme-endurance events (contrary to our now jaded sensibilities, a marathon IS extreme. An ultra-marathon is therefore really really extreme!)

Many people die each year participating in marathons and yet there is hesitation to come right out and say that related damage to the heart is not just "implausible" but inevitable and that this form of exercise should be looked at as something other than a "health" pursuit.

There is no difference between marathoning and any other extreme sport except like rock climbing, big-wave surfing, etc. Except, however, that the arbiters of conventional wisdom tend to prop up "cardio" as a health pursuit rather than the expression of will, determination, courage, and risk-taking that it is.

Perhaps they are afraid that if they tell people that it is unhealthy to run marathons then some people, in this country of rapant obesity, will stop exercising all together. I think that this is rather simplistic and avoids the real issue of our changing, technological, sedentarism-prone society but nevertheless, this may be a factor.