“It suggests that there’s some sort of tipping point for people beginning an exercise program. Initially it’s all hard work and no fun — but if you can stick with it long enough, you finally get fit enough that you can push yourself hard and long enough to get the flood of feel-good chemicals. And then — in theory, at least — you’re addicted!”
Sure, but that “all hard work and no fun” can be avoided by selecting the right intensity for the right duration so that it is hard work and fun.
Learn more about how hard to exercise.