I think it's pretty misleading to characterize "no going to the gym, ever, until further notice" as a simple action.

Why? It's a pandemic. If anything we're lucky it wasn't more deadly than it is.

I'm not gaining muscle mass but I'm having absolutely no trouble whatsoever maintaining it at home with exercise bands and calisthenics. It's a tiny, tiny price to pay for helping keep my community safe.

I would sacrifice the gym for the rest of my life if it meant adding even a year of life to a single person. Sentient existence is immeasurably more valuable.

I guess there's a values gap there I don't know how to bridge. I don't recognize the entire category of unbounded obligations to preserve life that you're suggesting.