(1) Movement, (2) purpose and (3) company. Going on a walk satisfies "movement", but it leaves out the other two. It's a good idea to try to involve more than one of the features - all three, at best!
Example: Doing an hour's walk, for a reason other than just doing a walk and do it, whatever it all is, in company. One image of this could be...doing a (1) walk, for (2) charity, with (3) others - that's movement + company + purpose. That's just one example, though...you could probably invent dozens of your own.