Do you know what your Diaphragm muscle is, or where and what it does?  So that we are all on the same page, its the muscle separating the intestines from the lungs.  a thin sheet of muscle attached at the bottom of the ribs that's designed to be the primary muscle for respiration.  On inhale it pushes down into the belly and on exhalation is pulls back up into the chest forcing the air from the lungs.  You know what else it does...... CORE STABILITY!! If you are not a belly breather, most of us are not, One of the biggest and best core muscles isn't being utilized which will eventually lead to core instability and low back or pelvic dysfunction.  So how do you work that particular muscle, I know I've never seen a "diaphragm" station in the gym!! Breath, yes, just breath! Lay flat on the floor with your legs elevated and just breath in and out of the stomach.  On a side note, if you have a problem with acid reflux, this may help with that as well.  The cardiac sphincter, meant to prevent acid backflowing into the esophagus is connected to the diaphragm.  If the diaphragm is weak would it not make sense the cardiac sphincter could be weak as well?  So if you get the diaphragm working right you could in-turn, stifle your acid reflux.