This post will make more sense if you watch the video first.
I disagree with one wording choice. A forward shoulder position is not pulling the shoulder out of it's socket.
The primary issue Jess describes is an overextension of the arm which can stress the shoulder. She notes this in particular for women. I don't doubt the association between this problem and women. In part because she makes a good observation that the shoulder blade wings out. Given that our society discourages women from engaging in actual strength training, especially for the upper body, it is not surprising that this is more common for women.
|An extreme example of scapular winging ("Wingingofscapula". Licensed under CC BY-SA 3.0 via Wikipedia.)|
The most common cause of this is weakness of the serratus anterior muscle. The serratus anterior has it's major role in keeping the scapula pinned to the ribcage. The muscle attaches to the underside of the shoulder blade, on it's inner edge and then to the ribcage around the sides. The muscle's action is to protract the scapula i.e. slide the shoulder blade forward and also to upwardly rotate the scapula.
Secondary to this is strength of the rhomboids and middle trapezius. These muscles attach to the inner edge of the scapula and then to the spine. As such they retract the scapula, that is slide it towards the spine. Therefore they can help stabilize the scapula, but only by preventing it from moving forward also.
Our focus then needs to be on the serratus anterior development. There are two basic exercises for this:
1) Push-up plus (scapular push-up): set-up for this exercise in a push-up position. Your arms will stay locked out during the exercise and the torso needs to be kept in neutral posture. Then squeeze your shoulder blades together and then push them out. This lowers and raises your whole body (which you are keeping locked into good posture.
2) Incline presses: any kind of exercise where you are positioned on an incline bench and pressing upwards will make good use of the serratus anterior. This can be done with dumbbells, barbells and other tools. Make sure to fully extend the arm upwards to get full motion forward of the scapula. And make sure to use enough weight for strength gains - that means enough that you can only do 12 or fewer repetitions.
The rhomboids and middle trapezius will assist the serratus in stabilizing the shoulder blade and so exercising them will also be of benefit. Exercises for these can start with basic upper back exercises like rows: one-arm, barbell, cable etc. Single joint exercises like reverse flyes can be added if more is needed; but usually it is not.
Forward, Rounded ShouldersJess also talks about having forward, rounded shoulders, which is common with folks who work at a desk job. People who have had this for a long time may have shortened there chest muscles and so stretches may help those folks. However, it's frequently more about attention to posture and ergonomics. Additionally, strengthening the back, as I just described, will help.
Jess also makes a good point here about making sure that when you are strengthening the pecs you also need to work the back, otherwise you end up with your shoulders pulled more forward.
That's only a brief look at rounded shoulders and I'll likely get back to it in another post.