Broken, not golden...

The only research I've hear of on the subject is for high level athletes that train at 20+ hours a week for years.  For the average age grouper there is not any evidence that I am aware of that you decrease you quality of life by training.  Common sense would say the opposite, that you have increased your life expectancy and lead a much healthier lifestyle.

All you have to do is look at Sister Buder, Hoyt and the 7X old athlete Frank (can't remember his last name) that are still kicking butt and living a healthy lifestyle and competing.

You may be interested in this - MSNBC piece discussing the results of one large study (over 24 years) regarding runners vs. non-runners:

http://www.arkansasrunner.com/misc/reason.htm

Chris

In a word - NO. Injuries may cause debilitation, but exercise and general fitness will not.  If your obese friends live long enough, their bodies will show more strain/wear since they are poorly conditioned.  This of course assumes that they do not succomb to heart attacks and strokes earlier.  Will your knees be "worn"? Not really any more so than a 300 pound person of the same age who lumbered between couch and fridge between commercials for some more ice cream and fried chicken. The body is in general equipped with the tools to repair minor injuries, otherwise we would never make past our 20's. 

The only grain of truth in their statements is that being physically active is likely to increase the risk of injury - both overuse and crash.  And that might cause some later debilatation.

I think those friends of yours are confusing "regular exercise and training" with "professional athletes who abuse their bodies".

Anyone who understands their body and train on a regular basis (while taking rests for injuries) will lead a healthier, longer and happier lifestyle.

On the other hand, you can look at a professional football player.  These guys go out there and train and abuse their bodies.  Most of these pros look amazing while they are playing, but the wear and tear they put on their legs and back (and playing through injuries during the season) will leave them permanently disabled in the long run.

Heck, just look at the numbers: 

-Most triathletes hit their "peak" in their 30's (I believe marathoners peak between 30 and 37?).  

-In 1986 the average "stay" of an NFL player was 3 years.  So around the age of 25! (pension/retirement for NFL players kicks in after 4 years in the league)

So I guess in some respects your friends could be right.  But when it comes to the type of training we all do (i.e triathlons) they are completely wrong.

X's 2 .... But please use Sea salt, its much better for you than regular salt.