When my dad was a boy, the idea of a gym (outside a school gym) was fairly unknown here. They were like, want to get stronger? Go kayaking. Want to lose weight? Play soccer.
Sports have big startup costs for most, but I agree that once they are paid a sport will tend to generate feelings of intrinsic motivation. Reducing those startup costs would be valuable.
With Alicorn's permission, I'm resurrecting this thread.
I'll start off with one of my own: What kinds of exercise can I do at home (I do have 5- and 20-pound weights), and what are good ways to get motivation to do so regularly?