Common Sense....

....would say that if a workout puts you in hospital, it's maybe not the most productive use of your time.

Some, apparently, would disagree.

Mr. Glassman, CrossFit's founder, does not discount his regimen's risks, even to those who are in shape and take the time to warm up their bodies before a session.

"It can kill you," he said. "I've always been completely honest about that."

from

http://www.nytimes.com/2005/12/22/fashion/thursdaystyles/22Fitness.html?_r=3&oref=slogin&oref=slogin&oref=slogin