Straighten up that back soldier! No seriously, if you are like the majority of the population, chances are you are suffering from symptoms correlated with bad posture. Catching a glimpse of myself in the mirror, it’s easy to see that I have forward neck/head posture. This is normally caused by a variation of weak neck muscles, seated job positions, incorrect sleeping positions, and prolonged computer or TV use. But other than the un-esthetic aspect of bad posture, there’s really not much to worry about right? Wrong.
Over time, poor posture takes a serious toll on your spine, shoulders, hips, and knees. In fact, it can cause a cascade of structural flaws that lead to back and joint pain, reduced flexibility, and compromised muscles, all of which limit your ability to burn fat or build strength.
Worst of all, bad posture can cause nerve constriction. As the spine changes in shape, the resulting movements or subluxations can put pressure on the surrounding spinal nerves. Because the nerves that connect to the spine come from all over the body, these pinched nerves can not only cause neck and back pain but may also cause pain in other unrelated areas of the body.
The problem: The sternoclavicular joints are unstable, therefore the body recruits the pectoris minor muscles to stabilize the joint. This brings the shoulder forward. With the shoulder forward, the upper trap turns on helping to support the shoulder from the neck. There is also a relationship with the thoracic spine & the sternum. The exercise described recruits global muscles to do the work of the postural muscles what happens is that for a short period of time holding through these muscles works then the muscles fatigue and the person falls back into the poor posture.
For the rest of the story: http://www.collective-evolution.com/2014/07/07/6-bad-postures-that-are-ruining-your-health-and-how-to-correct-them/