can too much exercise kill you?

A recent Chicago study apparently concludes that too much exercise can be deadly:

Too much exercise can kill you, scientists have revealed.

White men who work out at least seven-and-a-half hours a week are nearly twice as likely to suffer from heart disease than those who do a moderate amount, a new study shows.

Researchers in Chicago assessed exercise patterns over the course of 25 years and made the surprising discovery that very active white men are 86 percent more likely to experience a buildup of plaque in the heart arteries by middle age.

But this didn't apply to black men, they discovered.

It was suggested high levels of exercise over time caused stress on the arteries leading to higher coronary artery calcification - CAC.

However scientists warned people should not stop exercising.

The team from the University of Illinois at Chicago and Kaiser Permanente looked at the physical activity trajectories of 3,175 black and white participants in the longterm CARDIA study and assessed the presence of CAC.

The presence and amount of CAC, is a significant warning sign to doctors that a patient may be at risk for developing heart disease and a signal to consider early preventive care.

Dr Deepika Laddu, assistant professor of physical therapy in the UIC College of Applied Health Sciences, said: 'We expected to see that higher levels of physical activity over time would be associated with lower levels of CAC.'

However they found that at the top level of exercise, there was no extra risk for black men, but an 86 percent increased risk for white men.
Unique to the new study is the evaluation of long-term exercise patterns, from young adulthood into middle age.

It's almost circular to say that "too much" exercise can kill you: the moment you use the modifier too, you are, by definition, talking about something that passes a boundary, moving you from modesty to excess, or from safety to danger. So of course too much exercise can kill you: too much of anything can kill you. Viewed in that way, the article isn't saying anything revolutionary. The racial differences pointed out by the article are interesting, however, as is the number of hours per week defining the deadly threshold for exercise.

I walk about 3.5 hours per day, but I haven't been to the gym in weeks, so I'm not sure that all my walking qualifies as "too much" exercise.