In this video presentation Fred explains the relationship between these muscles, the shoulder blades and your posture.
For most people, proper posture in the shoulder area eludes them. But on many occasions when you’re able to get in touch and straighten up properly, you probably have briefly had a taste of that “sweet spot” of balance and stability. Although for much of the time, you probably slump over or you go to the other extreme and adapt a stiff military type posture, thrusting your chest up and forward while wrenching your shoulder blades back toward your spine. But we have all experienced times when our shoulder blade alignment is natural and relaxed, when none of the supporting muscles are contracted and tense or overstretched and weak; and then you feel amazing.
The challenge, of course, is first in finding and then in maintaining that posture. But it's worth all the effort; not only will you look better when you’re standing up straight, but you'll also experience fewer aches and pains in your neck and back region and you'll then be able to practice yoga asana more easily. When you spend too much time looking like a Marine at attention, you’ll notice the tightness in the muscles between your shoulder blades and that can make it harder to raise your arms over your head, whether you're reaching up high for that box on the top shelf or pressing back into the downward-facing dog pose, or reaching for the sun as in the tree pose. When your tendency is to slump, you will probably have a difficult time doing backbends and you’ll notice a limited range of motion in your shoulders.
In addition to the role they play in maintaining proper posture, the shoulder blades (scapulae) act as the foundation for your arms. The stability and mobility of your shoulder blades depends almost entirely on the muscles that are attached to them. Fifteen muscles attach to each shoulder blade, and their actions are obscure, so it’s best to focus on just two opposing muscle groups that are crucial for both good posture and complete shoulder function: the adductor group, which pull your shoulder blades toward your spine, and the abductor group, which draw them away from it.
If you find standing “at attention" is your default position, you need to re-educate the muscles that adduct your scapulae (the trapezius and the rhomboids) to relax and soften.
The trapezius muscles lie just under the skin and run from the base of the skull and the spine out to the shoulder blades, covering most of your middle and upper back. The middle trapezius muscles, whose fibers run horizontally from the upper/middle-back vertebrae to the inner edge of the scapula, does most of the work of pulling the shoulder blades toward the spine. It gets help from the upper and lower parts of the trapezius: Along with pulling the shoulder blade toward the spine, the upper trap lifts it, while the lower trap pulls it down. But those actions usually cancel each other out, so when the whole muscle contracts it pulls the shoulder blade toward the spine. Immediately beneath the trapezius lies the rhomboid. Running between the upper-back vertebrae and the inner edge of the scapula, this muscle exerts an upward pull as well as a strong adduction.
Several yoga poses can help you stretch your trapezius and rhomboids. While assuming the cat pose (Marjaryasana) or the child's pose (Balasana), you can breathe into the space between your shoulder blades to relax and lengthen these muscle groups. In the eagle pose (Garudasana), you'll feel both shoulder blades pull away from the spine, especially when you lift your elbows and your breastbone. After you unwind your arms, envision opening a space for your heart and lungs, not just from the expansion of your chest, but also by widening the space between your shoulder blades.