There are a lot of systems that function subconsciously in your body that you likely take for granted and very rarely, if ever think about; among the most important of these is breathing. It is an amazing physiological process that allows you to draw oxygen from the air and filter it into your blood stream to keep you alive. Your brain and spinal cord automatically just do it for you. You breathe faster when you run and slower when you sleep; it's a great deal, your body just figures it out how much oxygen you need and alters your breathing rate for you. The drawback of not being an active participant in your breathing pattern is that you can lose touch with what is 'normal' for your body and be unaware of how things like pain, stress and posture are affecting you.
A basic understanding of the biomechanics of breathing and posture will help you understand what I mean. Your ribcage and thoracic spine are the structural foundation of your torso. The rigidity of it protects your organs and supports your shoulders and neck, while the mobility of it helps you breathe, twist and move. Your lungs line the inside of your ribcage. In order for you to draw air into them, your ribcage needs to expand slightly and your diaphragm needs to contract and pull down; this will create a negative pressure and air will be pulled in. The elastic recoil of your ribcage and diaphragm passively push the air out to complete the breathing cycle. This keeps you alive.
There is a difference between being alive and breathing well. Just because you can breathe, does not mean you are doing a good job at it. Just because you can stand, doesn't mean you have good posture. Just because you can walk, doesn't mean you are using your body properly. There is a connection between how you breathe and how you stand due largely to the role of your diaphragm and the muscles in your mid to low back. Your diaphragm is a big muscular dome that connects and supports the lower part of your ribcage. It is an integral part of breathing, but it also has a major role in supporting your torso vertically from the inside. Poor use of the diaphragm leads to the torso tipping backward when you attempt to stand up straight. The result is compression and immobility of the lower back half of the ribcage. Unfortunately this is what most people do when cued to lift their chest up and pull their shoulders back and down. It opens the front of the ribcage, but closes down the back. The result is typically a chronically tight back, shoulders and neck with restricted lung capacity because the ribcage doesn't move well.
*Poor diaphragm use; tipped backward *Good diaphragm use; vertically stacked
The goal of good posture should be to vertically lengthen and stack the spine and ribs, but most people tend to lengthen their front and compress their back during day to day life postures, then work on compressing the front by doing sit ups and plank exercises during a workout. The result can be a strong, immobile, stiff ribcage that will force breathing to be either quite shallow or all in the belly and shoulders. If you go for a run and get your breathing rate up, you will notice that your shoulders lift up and down as you breathe and pant to catch your breath. The stiffer your ribcage is the more you will need to use these accessory muscles of breathing all the time, which tends to translate into neck and shoulder problems.
Learning to use the internal support structure of your diaphragm can be quite hard as most people are really tight in their mid-low back area which will inhibit the dome from lifting and opening the lower, back part of the ribcage. The best thing to do is to start with what I call the rib shimmy exercise to start and build awareness of the area. It will also really help to have the area needled, manipulated and or massaged to loosen the back muscles and joints.
Start by sitting down and looking at your side profile in the mirror. This lower part of your ribcage is the part of your back that will accommodate your neck, if you have a significant forward head posture; it is easier to sway the lower back forward to lift your head up than to actually lift your chest and head. If you do have a forward head posture or are really tight in your chest, drawing your lower ribcage back may feel like you are leaning well forwards; this is when a mirror is useful to see what your side profile looks like. Your body may be quite straight and just your head is pushed forward. Try to maintain your lower trunk position and attempt to lift your chest up. (Also see How to Sit)
Overly braced ribcage Good diaphragm support
Breathing effectively with your diaphragm should expand your ribcage laterally and posteriorly to broaden your torso; it should not involve your shoulders lifting up to your ears. As you take a deep breath, you should feel your torso lengthen and lift as your ribs pull apart, but this should not make you tip backwards. Learning to use this muscle more with occasional deep breaths will keep your torso more flexible, but using it to maintain the natural S-curve of your spine during exercise will help you engage your abdominals and protect your back, neck and shoulders.
Before breath Using diaphragm into sides/back Poor diaphragm
Pain, stress, emotion and attitude will affect how you breathe and how you hold yourself physically. Stress and pain tend to make people tense and breathe very shallowly, leading to further stiffness and more pain. Being very self conscious or very cocky is reflected in your physical posture, which can end up creating physical restrictions to breathing well that can lead to pain. Long story short, taking a few extra minutes to pay attention to how you breathe, sit and stand can have significant benefits to improving your pain and your posture. Learning to integrate the role of your diaphragm into your movement patterns will help you prevent injuries and maintain good posture.
Please watch the associated video with this post to see the movements and postures I am talking about.