As an exception to the normal situation we're considering, I've used gyms that were part of a gay bathhouse facility. And really quite modern, large and complete, comparing favorably with dedicated gyms. Not some crappy token workout stuff.
There the guys were not only shirtless, but in many cases bottomless, too. Or with a jock alone, especially when jogging on the treadmill. A bunch of guys working out nude, lifting weights and using the equipment, is a wondrous sight. And pretty good younger bodies, too - the older and out of shape ones generally wouldn't dare it. All fastidiously using towels on every equipment surface their naked skin would touch.
I also belonged to a gay naturist (nudist) club based in Minneapolis, called "Naked Minnesota". Can't do much that's nude outdoors in a northern winter, so monthly we'd arrange for special closed hours with indoor venues, like bars, bowling alleys (now that's a sight!), gyms, spas, etc.
Again, towels placed on everything you touch. It's great to be spotted by a guy standing over you naked on the free-weight bench.
Although one time, in order to have enough business to justify opening the place during off-hours, a spa owner made us agree to combine with another nudist group. That turned out to be straight, with female members. That was not so pleasant to see.
But hey, another one of my bizarre experiences I could add to my catalogue of memories. That I might title: "The Good, the Bad, and the Ugly".