Before you start working these areas, it helps to have a clear vision of how the arms and shoulders should be positioned. Think of Sarvangasana and turn it upside down. In a strong and spacious pose, the line from the shoulder to the ankle should be straight up and down, with the upper arm extended behind the body at 90 degrees. This position of the shoulder, with the arm reaching back behind the body, is called shoulder extension.
While the shoulder extension is a crucial element of Sarvangasana, it isn't something that everyday life requires of us. Therefore, many people don't have 90 degrees of shoulder extension. When they try to go there, the shoulders roll forward and contribute to the chest's collapse. You can see this by standing in front of a mirror with your arms by your sides. Slowly reach your arms behind you. As your hands move back and lift away from your buttocks, your shoulders will roll forward and down, drawing the breastbone and front ribs down and making your back ribs bow out behind you.
So how can you train your body to achieve a 90-degree shoulder extension in which your chest is open, your spine is beautifully straight, and the weight of your body soars upward? You start by working the muscles in an "unloaded" position, getting the feel of shoulder extension, while keeping the chest lifted and the shoulders in place without bearing any weight on the arms and shoulders. Again, stand in front of your mirror with your arms by your sides. Notice that if you internally rotate your shoulders—the inner elbow creases turn toward your side waist, and palms face backward—your shoulders move forward and down, while your chest collapses. If you externally rotate your shoulders by turning the palms forward, your chest lifts, the shoulders move back and down, and the shoulder blades pin in against your back ribs—just the position you want when you turn upside down in the pose.!--page-->