First, calling it “body movement” instead of “exercise” took a lot of the emotional freight out of the situation. I went to elementary school and junior high in the 1970s, where the typical gym teacher motivational strategy was to goat the hell out of one kid to motivate all the others. I was almost always the goat. That kind of persistent victimization leaves a mark. By the time I was 14, I was violently allergic to exercise and anyone who practiced it. So changing terms — reframing, in Lakoffian dialectic — helped me a lot.
Second, public reporting of my activity. I’m accountable to the world. Not that anyone’s keeping score (that I know of). It just means if I miss or slough off a day, I can’t rationalize it away or “forget”. I have to admit it, in print, in public. For me, that works well. For some, that would probably be a horror show.
Third, I convinced myself that body movement was and is an essential component of my writing strategy. If I don’t get out and move around, my energy levels are lower, I’m logier, I don’t have as much energy and focus to write. Once I was able to accept it as a writing-related program activity, just as important as story marketing, reading or research, then it became a lot easier to adapt my behavior.