I LOVE my GC2B, but I can't stand it at the gym. I would really recommend a sports bra for the gym unless it is unbearable to have (I understand having the mirrors everywhere and bulked up guys all around makes it tough to not bind!). But then I can barely stand the restriction of a bra while working out, so I might be biased. (Until i started binding, I never wore bras.) I simply can't stand anything inhibiting my breathing. But if you are going to bind, GC2B binders are my favorite of all the binders I've tried. I am not exactly huge chested (I was a 34C but have gone down to a 34B after losing weight), but it makes me totally, 100% flat. Like a board. It's the only binder I have found that allows me to wear any kind of shirt I want. Obviously it probably doesn't work so amazingly with larger chests, but the others I have tried didn't do much more than a compression sports bra even for my smaller chest. I have worked out in it and ridden horses in it and didn't collapse or anything, I just felt like I could have been working out harder if I could breathe a little better and I had to stop every now and then to take some deep breaths. Never got REALLY short of breath, though, just a feeling that I wasn't breathing as deep as I could.