I am going to be that guy: you shouldn’t wear a mask at the gym. It’s bad for you and, in addition, it’s quite useless.
Anyone that goes at the gym should expect to walk into a DNA database full of viruses, germs, bacteria, sweat, saliva, skin, hair, and other disgusting stuff. I’ll add that no unvaccinated person should go to the gym for their own sake.
Our vaccination rate is 54% and 58% for first dose. Our active case count is going up exponentially as expected. I am merely following CDC recommendations. My approach is to go first thing in the morning after the place has been cleaned, use it and then leave. This gym has only had one COVID case and that was in the infant daycare. A baby had COVID but apparently got it elsewhere and didn't spread it to anyone in the gym. Delta certainly is different though.
My other alternative is to go during senior hours but the camp kids are there at that time. That will end in a week or two. The nice thing about senior hours is that everyone is vaccinated. That was the biggest topic of discussion from February to May there.