Vetted franchises with clear pros, cons, and who & where each one fits.

The world's largest fitness franchise — a compact, keycard-access gym open 24 hours a day, a model built to work even in smaller towns.
A compact 24/7 gym with a worldwide club network — a lean, low-overhead model friendly even to an investor with no fitness background.

American boutique fitness with heart-rate-zone coached workouts — guided group classes, not a self-service gym.