It would just be cosmetic like most "bitcoin" businesses. A gym is a physical location, uses land, can only be "bitcoin based" in places where bitcoin is legal tender. The US doesn't let you "pay taxes" (rent land) with bitcoin, it's dollar based.
They could price it in Bitcoin while adjusting the price against dollar exchange rate fluctuations, or price it in Bitcoin at such a high price it stays profitable, or price it in dollars and let you pay in Bitcoin, but they can't actually run a Bitcoin business if you live somewhere that's not allowed (most of the world)