The rhomboids and serratus anterior.
Muscles can only contract. They, therefore, need an antagonist to restore a joint to its original position. With that in mind, let’s look at two muscles that impact your shoulder blades, your rhomboids and your serratus anterior. Squeeze your shoulder blades behind you and your rhomboids pull, push your arm outwards as if doing a pushup or making a punch and your shoulder blades will shift forward via your serratus anterior.
The rhomboids connect from the inner edge of the shoulder blade to the spinous processes of the upper thoracic vertebrae. If you spot a person trying to massage the muscle by leaning against a doorpost and rocking back and forth, you are watching a person trying to release their rhomboid. The rhomboids are particularly prone to forming trigger points
The serratus anterior originates from the first eight or nine ribs and runs behind the shoulder-blade to connect along the same inner edge of the shoulder-blade. On some sense, you can think of this as one big muscle with a scapula/ shoulder blade that floats on it. The muscle has been called the Boxer’s muscle in that boxers rely on and hence develop this muscle to develop a stronger punch.
The muscle looks like an angel wing –
This is Manny “Packman” Pachio and his serratus anterior muscles. Look at the ‘finger’ shaped muscles just under the pectoral muscles.
Things that can go wrong.
For the cyclist.
Because you support your upper trunk with your arms, your serratus anterior muscles can work too hard in supporting you. There is a chance that they overwork, shorten and begin to place strain on the rhomboids.
For the runner.
In my experience, the shoulders are often used to stabilize weak or imbalanced hips. If you get shoulder pain from running you need to look to the hips.
For the swimmer.
Swimmers often shorten their serratus anterior muscles. This especially happens to swimmers who spend lots of time training freestyle. It can be exacerbated by swimmers who only breath to one side (as I do). Spend some time doing backstroke and breaststroke to balance out muscle strength through the shoulders.
For people who spend lots of time in front of their computers.
If you roll your shoulders forward while working you will shorten your serratus anterior and strain your rhomboids.
Make sure you keep these muscles strong. Exercises such as rowing and pushups will do the world of good. If you have upper back pain, get potential tight spots on the rhomboids released and make sure that the person helping you knows how to release the serratus muscles as well.
Hope this helps.