Once you see how shoulders are put together, it becomes pretty obvious that they have some serious design flaws.
Let’s take a look.
A joint can be defined as any place where two bones meet and move. As such, every joint has two basic jobs:
1. Hold itself together
2. Allow movement
These are actually competing ideas since the “stiffness” that keeps your joints from pulling apart is, by definition, limiting the movement of the joint to some degree. Our joints are faced with the challenging task of restraining the two bones just enough so that they stay attached to one other. Therefore, every joint falls along a continuum between flexibility and stability. And every movement concentrated more toward one end of that scale sacrifices benefits received from the other end.
Both the shoulder and the hip are joints where a limb attaches to the torso, but that is where their similarities end.
Hips are incredibly stable joints, with nice, deep sockets that help lock the head of the thighbone in place. Shoulders, on the other hand, have only a suggestion of a socket—so shallow that it’s basically like a golf ball sitting on a tee, offering hardly any “built-in” protection or stability.
Also, hip joints are equally surrounded on all sides by big, powerful muscles that can generate massive forces, take a beating, and still keep the joint snug and secure. Shoulder joints, on the other hand, are surrounded by much smaller and weaker muscles, making them much more prone to dislocation and injury.
But, these differences simply illustrate how hips and shoulders are specialized for their unique jobs.
Hips carry a much bigger load, so it makes sense that thick ligaments, deep sockets, and powerful muscles would make solid design features. Conversely, since shoulders generally carry lighter loads, it makes sense they would trade a little stability for some extra mobility. This makes shoulders much more versatile and able to perform a huge variety of movements through a much bigger range of motion than is possible at the hip.
Since the shoulder has sacrificed some security for mobility, the job of protecting and securing the shoulder falls on the muscles that attach around it. This is where the rotator cuff comes in to play. The rotator cuff is a group of four muscles that attach in a ring around the shoulder joint—like a cuff. Their job isn’t to move the shoulder; it’s to secure the shoulder while it’s moving.
Essentially, the rotator cuff muscles fire off like retro-rockets on a spaceship, coordinating their actions to help maintain the correct “attitude” of the shoulder joint within its shallow socket. In this way, the rotator cuff makes up for the relative lack of built-in stability of the shoulder by providing dynamic stability, ideally able to make split-second corrections as needed to protect the shoulder joint.
The real problem with shoulder design is that the muscular support is hugely imbalanced. While the shoulder does have a team of muscles around the joint whose job it is to equally support and secure it from all directions, some of those muscles grossly overpower others. And if one muscle overpowers another in the shoulder, it can pull the joint out of position and allow for a rotator cuff injury, a labral tear, a sprain, an impingement, a separation, or even a dislocation.
Specifically, there are two groups of muscles that commonly run unchecked:
2. Internal rotators
Protractors are the muscles that pull your shoulders forward, like when you slouch. Internal rotators are the muscles that press your palm against your belly or down on the top of a desk.
These two muscle groups are greater in number, size, and strength than their antagonists, whose job it is to restrain and “moderate” them. Not only that, but since your eyes face forward and your hands are designed to grasp in front of you (rather than behind you, which would use retractors and external rotators for), everyday tasks like picking up objects, washing your hands, driving, and typing on a keyboard all exaggerate this imbalance even further since they all primarily use—you guessed it—protractors and internal rotators.
Average folks with healthy, painless shoulders have internal rotators that are 33 percent stronger than their external rotators. However, a study of 125 professional baseball pitchers (who use their internal rotators to throw all day), found that, for them, this imbalance was hugely magnified—with internal rotators clocking in at a staggering 93 percent stronger than external rotators! This tells you the scale of the imbalance that may exist in your shoulder, especially if your sport or workout of choice pushes you even farther in the wrong direction.
Now you know why I said your shoulder was designed to fail. But there is a solution, and it’s a fairly easy one.
It’s simply a matter of finding deficits and addressing them. For example, since we know that you’re starting off with strength deficits in your shoulder retractors and external rotators, strengthening them merely means incorporating retractor and external rotation exercises into your weekly regimen. This will help ensure that your shoulder is far more protected—and functional—than it was before. Be sure to consult a doctor if you have sharp pain that won’t go away or pain that is worsening. It’s better to know early if something serious is wrong than wait for it to worsen.
Although your shoulder may have been designed to fail, it’s not that hard to prevent its failure. Try working on your external rotators and retractors and see how big a difference it can make—both in how your shoulder feels, and in how it functions.
*This article first appeared on Dr. Bockmann's website, austinspineandsport.com.