I know it’s muddy because there’s some overlap, but this thread should stay more focused on your experiences with masks in the gym - its original topic - and not general opinions on the need/benefits/complaints about masks and those types of related issues.
That discussion belongs in the long-running Coronavirus thread here: Coronavirus - What Happened?
On topic, I have no experience lifting in a mask since I haven’t been in a commercial gym in over a year (cancelled my membership just a few months ago, actually, one reason being their “loose” [to put it generously] safety protocols).
I’ve had the mask on during quick-paced half-hour walks, 2+ hour shopping trips pushing a loaded wagon, and recently a few Home Depot trips pushing an overloaded flatbed cart with a metric shitton of rock and sand across the parking lot a’la Prowler work. No, the double-mask (disposable mask under a cotton mask) did not cause me to become more winded than usual.