The most important feature of exercise is that the participant is not doing something unhealthy in place of it. For example, slowly walking around the neighbor

The most important feature of exercise is that the participant is not doing something unhealthy in place of it. For example, slowly walking around the neighborhood over a period of two hours is awesome--even if it's low-impact. Slow, low impact exercise benefits everyone, even superstar athletes, even if all it does at that level is simply keep an athlete away from trouble. Same deal for people who are out of shape. Proceeding along the same line of thought, even slow, low-impact exercise benefits participants in avoiding the reinforcement of unhealthy behavior. Not only is one avoiding a day of a bad habit, but they're helping to completely break the habit, as well. Next, of course, is that any slow, low-impact exercise helps the body replace previous bad habits with new ones. Future exercise is easier to do. One cannot just break a habit; they must find something else to do in place of it. What is exercise? One can say that it's an activity that isn't unhealthy, regardless of specific activity. If one can't call an activity "exercise", then very likely, not only is it not neutral, it's specifically unhealthy. Otherwise, it would be called exercise--walking, jogging, dancing, swimming, participating in team sports, strolling, mowing the lawn, working outside, etc. Activities that cannot be described as physical exercise should be replaced with those that can, and they don't have to be super strenuous. I think exercise has evolved to mean "running for twenty minutes a day, three times a week" when it can also be "five hours of any kind of bodily motion every single day."