Maybe we're addicted. It might be true, but pardon me if I'm a little skeptical. It's not that I'm unhappy running, I just don't see myself ever twirling around and singing a' la Julie Andrews in the opening scene of The Sound Of Music. Pencil me in as unconvinced on the endorphin issue. I suspect that the whole theory was the brainchild of some well-meaning, yet overzealous runner bent on making workout converts out of couch potatoes who grew up in the 60's and 70's.
Runners find it easier to work additional physical pain into their routines as opposed to rest.
The word got out that training at high altitude improves performance, and the populations of Boulder, Albuquerque and Flagstaff increased immediately with wheezing, breathless runners. Reports stated that conditioning the body to handle heat resulted in faster times, and runners started resembling the Michelin Man in their workout attire. We thrive on suggestions which challenge us or threaten our personal comfort in some way. We read about the Kenyans' killer hill workouts and instantly begin calculating a change in our training loop. Henceforth it will include a grade which can only be ascended by using our hands as claws in the surface of the pavement.