Endurance Sports, All Pain or Part Euphoria?

As an endurance athlete pain is par for the course. Not the pain of injury, but the sweet pain of progress.

I stumbled on an interesting article from the New York Times, that discusses pain and discomfort during exercise, and what makes the athlete stop.

http://www.nytimes.com/2011/05/17/health/nutrition/17best.html?_r=4&emc=eta1

Also, it brings up the euphoria that most of us have felt at one time or another. The feeling you have after a hard interval session, or a long run. You lay on the couch completely spent, and elated at the same time.


Your thoughts?