I don't get why you're downvoted. I think it's a creative idea. But I don't think it will fly (pun intended). Real estate (as in space) on a plane is probably

I don't get why you're downvoted. I think it's a creative idea. But I don't think it will fly (pun intended). Real estate (as in space) on a plane is probably the most expensive in the world. While airlines reserve space for (for example) a bar in business class (and to the best of my knowledge only in the A380) a gym would use too much space. There's also the issue with turbulence to consider, which would make a gym (at least without significant adaptions to the machines) rather impractical.