I've been researching a lot of past articles here on posture and muscle balancing, and I've found that my posture kinda sucks, especially upper-body-wise. Specifically, My shoulders are too rounded, my upper arms rotate inward, and my torso tends to kinda sag forward overall at rest. Actually not all that uncommon, as most people I see have these postures.
So ..... in trying to correct that, I make a concerted effort to walk and sit with proper posture. Back straight, chin back, shoulders retracted slightly to compensate for their internal rotation. Ends up my abdomen gets tucked in in the process; nut sucked in like I'm trying too hard to impress chicks on the beach -- just tucked in. Not a bad thing because I've always hated the saggy abdomen, but it does a number on my breathing. Specifically, it always seems like I'm short of breath if I'm not breathing through my mouth -- something I don't normally do.
Am I doing something wrong, or would this just be my lungs having to breathe differently due to the change in shape of the thoracic area. Also feel free to comment on whether or not my notions of proper posture are correct, as this is something that I've never really dealt with. And it shows, trust me.