Did you realise a lot of your lung capacity is at the back of your body? To make the most of it, we need to have good posterior (back) rib cage expansion.
Try this. Place your hands around your ribs with the thumbs facing forward and fingertips cradling the back ribs (if your shoulder mobility allows). Take a few breaths and notice whether you are feeling ribs expand underneath your fingertips as well as at the front where your thumb is. This might be tricky for some.
If you do feel expansion, now start becoming aware if your shoulders seem to be activating as you breathe into your back ribs. They should not be, ideally. If they activate, you might be doing this without conscious awareness during the day as you breathe, and this can contribute to shoulder tension.
To improve your lung capacity, free up your back rib cage breathing and liberate your shoulders, come and talk to me