Years ago, exercise physiologists thought that you could become addicted to exercise, much like you could addicted to morphine. Vigorous exercise causes an increase in your levels of endorphins. The name endorphin comes from combining the two words endogenous (made in your body) and morphine, and these chemicals act on the same receptors as narcotics. Endorphin levels go up with most bouts of intense physical activity. Scientists used to think that endorphins accounted for a runner’s high and explained why someone could get addicted to exercise.
Most intense workouts cause an increase in endorphin levels. One of the exercise studies showed that weight lifting causes your endorphin levels to go up, similar to the increase from running on a treadmill. Our bodies make endorphins whenever we exert ourselves, and the higher levels probably help us better tolerate discomfort. Imagine that you are one of your ancient ancestors and running away from a wooly mammoth. You want to be able to keep sprinting and ignore any physical pain, at least until you are safely back in your cave. That is where endorphins come in handy; they help block out physical discomfort. Despite higher endorphin levels, most people do not feel high after or get addicted to exercise.
