Okay, so Planet Fitness isn't really a planet. But I do live relatively close to their national headquarters, so I figured it would be okay if I wrote about them. It was founded in 1992 for occasional or inexperienced gym members and is a "Judgement Free Zone." Which means that humans can't possibly work out there. Which means it must be gym for aliens!
Here's what I think happened:
Planet Fitness, in a galaxy far, far away, was faced with a serious disaster. All fiber and nutrient producing plants were struck with a massive plague, and only the sugar and fat producing plants remained. In addition, gravity was slowly decreasing as the planet continually lost chunks of its mass to the knawing darkness of space (that was because a really irritable group kept blowing pieces of it up). The predominant species, the Judgementafreeze, began to desperately struggle for survival and health - unable to eat properly and unable to exercise properly. Slowly, they grew rounder and fatter, cursing their inability to find health.
Then, one far-thinking group of Jugementalfreeze from the country of Workoutzone on Planet Fitness, had a brilliant idea. Stasis pods. If they could put themselves on a spaceship and launch it towards a compatible planet, they could live in stasis until arrival. At this new planet, they could then find good food and good exercise, and live happily for many generations.
Enter, Exeter, NH, USA, North America, Earth, Milky Way Galaxy. In 1965 there was an unexplained UFO sighting. Flashing red lights, a flying vehicle, a young Navy private, and two police officers... It's called the Exeter Incident. Look it up. Well, you can guess what the real story is. It was the Judgementafreeze trying to find a place to land. They eventually did, carefully hid their spaceship, and began the process of integrating into human civilization. In 1992 they figured out that they could capitalize on capitalism and started the Planet Fitness franchise.
That's why, if some of the people working out next to you seem like aliens, they probably are.
In conclusion, watch out for aliens at Planet Fitness.