I've been noticing in the past 3 or so years (I'm 17) that when I twist my upper body or move my shoulders up and down, opposite each other, that I either inhale or exhale sharply, like I'm gasping. I'm not controlling this, it happens even if I hold my breath, however it only occurs if my mouth is open. I do not have asthma or other breathing problems, though sometimes I do get short of breath after running. I have not had any running experience with sports or other activities however, so the two things may not be related. I was wondering what could be causing this sharp breath to happen?