Albeit, the above is the beginning of Abbott & Costello’s famous ">‘Who’s on first?’ routine the same scenario plays out when naming the muscles of the shoulder. In the first part of this series we discovered that the shoulder sacrifices stability for mobility making it prone to injury; we will now explore the ‘players’ responsible for stabilizing the shoulder joint.
Who's On First?
On first base is the popular crew which includes pectoralis major (pecs), the deltoids, biceps, and triceps. These guys work together to keep the arm close to the body and toward the front. Pectoralis major is important when your arm is overhead because it pulls the down and in tight towards the chest. Remember, your arm will come out of socket about two inches. Should you have weakness in any of these muscles (mostly deltoids) then you will encounter difficulty with raising your arm.
What's On Second?
The major stabilizing function for the traps is to pull the shoulder blade back towards the spine. Likewise, the rhomboids, which lie under the middle fibers of the traps, pull the shoulder back towards the spine. As a result, the lats, that large muscle of the lower back, does the same motion. It is important to note here that the back muscles are antagonists to the pecs and other muscles of the popular group. This makes it very important to strengthen them in order to maintain balance between the two groups of muscles.
I Don't Knows On Third
Time for the juicy part. Our third group is known as the rotator cuff muscles. If you haven’t gotten tongue tied with muscles names yet, take a stab at this. The four muscle that create the rotator cuff conglomeration are: infraspinatus, supraspinatus, teres major, and subscapularis. (Phew!) Most of these muscles are small in comparison to the other groups that stabilize the shoulder. You have been using these all your life, especially when you started crawling. This is important to note because our bodies are amazingly efficient at adapting so that as we continue to load these small muscles, everything else takes up the slack when weakness becomes present. For awhile you will likely not notice but over time your joint will start sounding like Rice Krispie’s cereal and before long you will find you are not engaging in activities due to discomfort.
The rotator cuff muscles stabilize the head of the humerus (ball of the shoulder joint) in all directions of movement while the other groups (popular & back) assist in these motions. Problems occur when the larger muscles (front & back) are not properly engaged to take on the load and assist the rotator cuff muscles. Think of it as asking a friend to help you move your couch and they agree. However, what really happens is they simply sit on the couch, eating chips, and tell you what you should do to move it out of your house. You can see why most people have shoulder problems.
The Shadowy Figure Lurking In The Dark
We have covered a lot of different muscles, but there is one lurking behind the scenes that is overlooked, not well known, but immensely important. Meet serratus. Serratus is located on the inside of your shoulder blade, but splays out to the ribcage. You can view portions of it by raising your arm overhead and looking at the ribs near the armpit. Those fingerlike muscles are the serratus. What does it do? If you can’t hold your arms out, then you have an issue with your serratus.
We have covered the anatomy of the shoulder and hopefully you didn’t sleep through it. Take a deep breath, review the material, and the final installment of this series will cover strengthening and stretching to build shoulders of steel.
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Kerry M. Davis LMT, CIMT, SFG