Sigh. The "endorphins" explanation of "runner's high" is just one theory; it is not widely held by those running daily, though it is widely cited by those suffering from the "little knowledge is a dangerous thing" problem.
I agree that the high may not be brain chemicals. Just revving up the body at triple intensity and getting all that blood and oxygen pumping contributes. Humans have been running animals for several million years. When you exercise your innate nature you feel good.
