I never said I worked out in it, or wore it to the gym. I said it wouldn’t be unheard of in a gym locker room, or changing room, whatever. The garment has to be worn at all times except for the 4 S’s, sweat (the gym, strenuous exercise, etc), swimming, showering (or bathing, whatever) and sex. What I meant was that I would go to the changing room, change out of the garment, into gym clothes, and exercise, then shower and change back into street clothes when I am done.
Also, I know many many people who wear undergarments very similar to the LDS garment. My grandfather’s and father’s boxers and white tshirts would be almost indistinguishable except for the markings on the garment. (They are Baptist). Over time, society has moved more and more towards skimpy underwear (whitey tighties, etc), but it isn’t universally that way.