Working Out/Exercise/Manic Intensity, Pushing Oneself

Not all "addictions" are necessarily bad.  Think about an exercise addiction--one is compulsive about exercising.  You've heard of marathon runners, but there are also "Ultra" marathon runners, who do, for instance, a hundred mile run, overnight!  They must be receiving lots of positive feedback that goes beyond a) transformation of body image and b) comes from within, because I believe there must be a threshold, maybe 10 mile runs, three times a week, wherein we'll hit peak body image.  Maybe I'm wrong, and I underestimate the continuum (and extremes) of body image, and the lengths people will go to achieve a certain perceived stature.  Still, consider that some people exercise far and away more than they must to achieve the body image that they desire.  The reason must be simple discipline: they like to push themselves; they like to see how far they can get; they like to know they can get up and do something that's relatively unique.  I think these are all commendable characteristics.  I do have a cynical viewpoint about this that I'm not expressing.  Mostly, that cynical side is sitting on the couch, eating chips, or telling me something about being productive in other "more" meaningful ways, but, that's interesting: who creates meaning for us?  Why must it follow a certain framework of utility?  Why can't it exist for a moment (or a run) and that's it?