The shoulder joint is one of the most dynamic and intricate joints in the entire body. Every time you pick up a barbell from the ground or drive one overhead a complex network of muscles, ligaments, and bones must work perfectly in sync with each other to keep the joint safe. A healthy shoulder is naturally mobile enough to move into a wide range of positions (like those needed for complex movements used in weightlifting and CrossFit). Although the shoulder is naturally mobile, this natural mobility can lead to future injury if the right muscles surrounding the shoulder joint are too weak.
In all my years working with athletes, the shoulder continues to be one of the most frequently injured joint in the entire body. In fact, research shows it is the most injured joint by those who lift weights competitively and recreationaly.1-4,10-11,16
Today I want to briefly go over the anatomy of the shoulder and cover some common shoulder injuries I’ve seen in the weight room.
Shoulder Anatomy 101
The shoulder joint is considered a “ball and socket” joint, made up of three bones: the humerus, scapula and clavicle. The end of the humerus (upper arm bone) is shaped like a small ball that fits into the socket of the scapula (shoulder blade). Unlike the relatively deep “ball and socket” joint of the hip joint, the socket of the shoulder is very shallow (this is why the joint connection is often compared to a golf ball sitting on a golf tee).
The “ball” of the humerus is held into place on the “tee” or socket of the shoulder blade (called your glenoid) by a number of small but very important tissues (ligaments and capsule). These tissues wrap around the joint like a tight fitting glove and form an air-tight hold on the joint.
Right over the top of these ligaments and capsule runs the the rotator cuff (a group of four small muscles that run from the shoulder blade and attach to the humerus). Because these muscles lie close to the joint and act to compress the humerus in the socket as the arm moves, they are therefore considered to be “primary stabilizers.”
There are then a number of large muscles that attach to the shoulder blade and/or humerus to help move the arm. The lats, pecs, and deltoids are big muscles that are often referred to as “prime movers.” You can walk in to any gym and see people (especially young males) working religiously on getting these muscles bigger and stronger. These larger muscles are often referred to as “prime movers.”
As we move throughout our day and lift weights during our workouts, the shoulder joint is most efficient when the “golf ball” of the humerus remains in the center of the “tee.” This is much easier said than done. As simple as this concept seems, at any given time only 25-30% of your “golf ball” is in contact with the “tee.”5,13 However, despite this very small coverage, a strong and healthy shoulder will actually maintain the ball of the humerus to within a few millimeters of the center of the socket throughout almost all arm movements!13
But how is this possible? This movement precision is the result of perfect interplay of two factors: static and dynamic forces.
Static forces describe the pull or tension created by structures we have absolutely no control over (like the ligaments/capsule that surrounds the joint and the labrum that expands the joint socket). The tension these tissues create combined with the shape of the joint socket is what dictates the degree of “passive stability” for the shoulder.13
If you’ve ever seen someone who is “double jointed” (extremely flexible) it’s often in part due to having very lax or loose static structures in their shoulder. It should come as no surprise that each of us have slight differences in our anatomy. When it comes to the shoulder joint, some people will naturally have more or less stiffness in their ligaments/capsular tissues as well as a different shape to their joint socket (some more deep like a bowl and others more flat like a plate.). Both of these factors can have great impacts on the amount of stability someone has.
For example, as you pull a barbell over your head during a snatch or jerk the joint capsule tightens or “winds up” to stabilize the joint and keep the humerus from falling sliding out of the socket. Those with a lax or loose capsular tissues (or a shallow plate shaped joint socket) will have less natural passive stability and will require even more “active stability” (from the muscles that surround the joint) or else they risk injury.
While we obviously can’t change how these static stabilizers work short of surgery, we can make sure the muscles that surround the shoulder joint (the active stabilizers) are doing their job.
When the small and large muscles that surround the shoulder turn on to control the joint they create dynamic forces. As mentioned earlier, the four small muscles called the rotator cuff (subscapularis, supraspinatus, infraspinatus and teres minor) surround the joint and create compression to maintain the center of the “ball” on the “tee” as you move your arm. These muscles work together with the larger muscles that attach to the arm and shoulder blade to produce safe and powerful movement whether your picking up a bag of groceries or throwing a loaded barbell over your head.
To understand how the dynamic forces of your shoulder work, imagine a young boy helping his father set up a tall ladder. The boy kneels at the base of the ladder, firmly securing it to the ground. The father then pushes the ladder upwards, leaning it against the side of their house.
This illustration is precisely what happens at your shoulder every time you move your arm!5The young boy is similar to your shoulder blade in this analogy. The rotator cuffmuscles work together to help to “steer” your arm into place by keeping the base of the humerus in a stable position on the socket while the stronger and more powerful muscles (like the deltoids, lats, and pecs) move the arm.
The two actions (one holding the base of the ladder in place while the other moves the ladder) working in concert is how shoulder dynamic stability is created and maintained. Without sufficient passive and active stability, we risk injuries like rotator cuff tendonitis and tears, labrum tears, or shoulder instability injuries (to name a few).
Simple enough, right?
Unfortunately, the shoulder complex is a little more complex. Not only do we need to understand the mechanics of the shoulder joint itself but we also need to take into account how the shoulder blade is moving! As you move your arm over your head, the shoulder blade moves as well in order to maintain contact with the humerus bone.
If we return to the prior analogy, think of what would happen if the father decided to grab the ladder and move it to a different part of the house. The ladder would potentially topple over if the boy didn’t get up from his kneeling position and move with the ladder to secure it back in place to the ground. Just as the boy moves to keep the base of the ladder connected to the ground, we must also move our shoulder blades to accommodate for the continued changing position of our arm bone. This action comes from a number of muscles that connect to the shoulder blade (like the rhomboids, traps, teres major and serratus anterior).
In order for the shoulder blade to move as it should, we also need to take into account one more important piece of the puzzle: the thoracic spine or mid-back. Because the shoulder blade is basically floating on top of the spine, the shape of the mid-back can dictate the efficiency (or lack there of) of it’s movement. In order for the shoulder blade to move correctly and be in the right place at the right time to provide stability for the arm, it has to easily glide on the upper back. This requires a certain amount of thoracic spine extension!
The architecture of the mid-back is naturally stiff and stable. It has to be stiff as many of the ribs that connect to it provide sufficient protection for our vital organs that lie close by. Unfortunately, the poor postures many of us assume throughout the day have led to the adaptation of a stiff or “kyphotic” and rounded upper back. When the upper back is rounded and unable to fully extend, the shoulder blade is limited in how much it can move.18 An immobile shoulder blade then affects the mechanics and stability of the shoulder joint itself. As you can see, there are many factors behind safe and efficient movement of the shoulder!
So to wrap this whole section up, here’s the basics of the shoulder complex you need to remember. If the shoulder blade moves as it should on top of a mobile thoracic spine, the rotator cuff muscles are able to do their job and maintain sufficient stability of the joint. The arm is then moved by the large prim movers of the upper body. Basically if every part of the symphony plays their part correctly, the “ball” stays in the middle of the “tee” and injury is averted.
So to the question ‘what causes shoulder pain?’ The simplest answer is that pain is often the result of excessive stress or strain on the small structures that surround the shoulder joint. The normally harmonious shoulder complex can be derailed by one piece malfunctioning (i.e. weak rotator cuff, poor passive shoulder stability). For the strength athlete, these forces are usually the result of cumulative micro-trauma due to three things:
- Imbalances between the prime movers and prime stabilizers
- Poor movement and lifting technique
The specific injury that is sustained (rotator cuff tendinopathy, labrum tear, subluxation, etc) depends on how that control and balance is lost. Let me explain.
Imbalances and Instabilities
In order for the shoulder to work correctly, the small “prime stabilizers” (rotator cuff muscles) must work in balance with the larger “prime movers” (like the deltoid). If these forces are not properly balanced (between either the prime movers and stabilizers or between the posterior and anterior rotator cuff) the stability of the joint decreases and the mechanics of the shoulder is thrown off.13
A common injury that occurs due to an imbalance like this is impingement. Research shows there are technically two kinds of impingement: external (or subacromial) and internal.15
When you look at the anatomy of the shoulder joint you’ll notice there isn’t a ton of space between the “ball” of the humerus and the structures that lie directly above (like the acromion of the shoulder blade).
External impingement describes the pinching of the the bursa (a small fluid filled “air bag”) or rotator cuff tendons against the ceiling created by the acromion bone. The subacromial space is the space between the acromion and the rotator cuff/soft tissue structures. Internal impingement occurs when the tendons of the rotator cuff are pinched between the “ball” of the humerus and the edge (usually the back side) of the socket “tee.” Because these classifications are based on where the impingement occurs, they often bring out pain in different parts of the shoulder.
External impingement for example often creates pain on the front side of your shoulder as you raise your arm overhead. Internal impingement creates pain on the backside of the shoulder as the arm is elevated and externally rotated.
Impingement injuries can also be classified based on the cause behind the pain (or pathomechanics). The pinching or impingement of the overlying structures in the joint can happen for two main reasons:
- Anatomy (primary impingement)
- Dynamic Imbalances (secondary impingement)
The first factor is the anatomy of the shoulder blade. The acromion in most people is fairly flat or slightly curved. However, for some people the bone takes a more hooked shape which can lead to less “free space” for the rotator cuff tendons and bursa as the shoulder moves. If someone has this type of anatomy and is forced to push through uncomfortable and painful positions (either by a coach or through their own self doing) it can lead to swelling of the rotator cuff tendons and even more narrowing of this subacromial space. Less space means more pinching of these tissues against the bony ceiling of the shoulder. With enough time, this micro-trauma can turn into a big problem like a rotator cuff tear.
Unfortunately, this anatomy is something we cannot change short of surgery. Early recognition of symptoms is key for getting ahead of this injury before it’s too late. Working with a physical therapist or coach to modify your lifting technique to fit your anatomy (such as taking a wider grip on the barbell for the snatch or jerk) may allow some to continue lifting overhead with less impingement.
The other (and more common form of shoulder injury in athletes in my experience) is secondary impingement. If you remember back to the start of this blog, I mentioned the shoulder joint is a “ball & socket” joint. That wasn’t 100% accurate. You see, when the shoulder moves into extreme ranges of motion (like lifting your arm over your head) the arm not only rotates in the joint, it also glides slightly forward, backward, and up or down. A secondary impingement doesn’t occur because of a structure abnormality but instead because of a functional problem. Usually an athlete will have difficulty maintaining adequate shoulder stability or they have excessive movement of the humeral head (ball) that leads to pinching).
These secondary impingements can be created by:
- Muscle imbalances
- Mobility restrictions
- Coordination problems
Muscle imbalances is the most common reason for secondary impingement. If the rotator cuff is not firing correctly or just plain weak, the stronger muscles (prime movers) that surround the shoulder will overpower the primary stabilizers (rotator cuff). Just like the small boy failing to secure the ladder to the ground as his father pushes it upward, this imbalance allows the humerus to move excessively from the center of the joint socket and smash the smaller structures that lie above it.
Mobility restrictions can also create impingements. For example, I find a number of strength athletes develop inflexible/stiff lats or pecs (also excessively stiff thoracic spine) which can restrict the arm and shoulder blade movement. When athletes have mobility restrictions, this can negatively affect overhead barbell or dumbbell lifts.
In order to maintain proper upper body tension and stability for pulls and deadlifts the body activates the powerful lat muscles (the huge “V” shaped muscles that run on the sides of your back). These strong muscles not only help create sufficient core stability and torso stiffness but also help maintain internal shoulder rotation to keep the bar close to the body as the barbell is pulled from the floor.
However, in order to move the barbell overhead the body also requires enough flexibility in the lats. In order to keep the humerus in the center of the joint as the arm moves overhead, the humerus must externally rotate. However, if the body has developed stiffness in the lats, the shoulder will be unable to externally rotate enough in the joint and impingement can occur. Those who have limited overhead mobility due to flexibility restrictions yet continue to force their shoulder into poor positions when lifting end up creating tiny amounts of micro trauma and eventual pain.
Proper coordination between the shoulder blade and arm is crucial to maintaining stability. As we discussed prior, the shoulder blade must move in sync with the arm. If, for example, the shoulder blade is unable to rotate upwards enough as the arm moves overhead (due to a weak or poorly functioning serratus anterior muscle) the humerus will shift excessively in the joint and impingement can occur.
Secondary impingements (as well as other more serious injuries) can also be caused by another mechanical problem, shoulder instability.17The term “shoulder instability” itself is a fairly vague term in part because it is difficult to determine whether the amount of mobility an athlete presents with is normal or problematic. Some athletes are extremely mobile. This “hypermobility” can be congenital (meaning you were “born loose”) or acquired over time (basically the small structures of the shoulder were “torn loose” due to repetitive micro trauma).8,12
Research has shown that anywhere from 5 to 15% of people are born with hypermobility (more often females compared to males).8An easy way to assess whether or not you fall into this category is by using the Beighton criteria screen.9
Try these 5 screens. For every screen (except the last) try it on both sides of your body and give yourself a score of one if you can perform the task and a zero if you cannot (total scores then range from 0-9).
- Grab your opposite hand 5th finger and pull it backwards as far as possible (be careful and don’t hurt yourself). Can you move it past 90° without pain?
- Grab your opposite hand thumb and pull it towards your forearm. Can you touch your forearm without pain?
- Straighten your elbow as far as you can. Does it hyperextend (past 10°)?
- Straighten your knee as far as you can. Does it hyperextend (past 10°)?
- Bend over at your hips and try to touch the ground without your knees bending at all. Can you rest your palms of your hands on the floor?
What did you find? Research has shown that those with a total score of 2 or more are likely to be hypermobile and are nearly 2.5 times more likely to have an instability injury of the shoulder!9
Acquired joint hypermobility on the other hand isn’t something you’re born with but instead is something that is developed over time. This kind of mobility is commonly seen by those who participate in sports where the same movements are performed over and over again resulting in excessive stretching of the static structures that stabilize the joint. For example, this is often seen with baseball players and gymnasts due to the repetitive overhead motions during training and competition of their sport.
Now here’s what you need to understand. Joint hypermobility is not inherently dangerous. There are plenty of athletes who have hypermobility (either congenital or acquired) who go their entire athletic careers without injury. If, however, a hypermobile joint fails to be controlled for by the dynamic structures that surround it (like the rotator cuff muscles) the shoulder can become unstable and injury will likely occur. The ability to dynamically stabilize the shoulder is the difference between functional hypermobility or pathological instability.
So how would instability lead to an injury when lifting weights?
CrossFitters and weightlifters are similar to baseball players and gymnasts in the sense that having the requisite shoulder mobility is paramount. The repetitive nature of lifting weights overhead in this manner can place the shoulder at an increased risk for injury especially if instability is present. While you likely won’t see a traumatic dislocation during either of these maneuvers, tiny amounts of micro-trauma are sustained at the shoulder if sufficient stability is lacking.
Because the shoulder is naturally a mobile joint, the location and specific type of injury can be different from person to person. It all depends on the direction the “ball” or humeral head moves off the “tee” or genoid fossa. For example, let’s go back to the injury of internal impingement. If someone has natural hypermobility of their shoulder joint and not enough muscular control, the tendons of the rotator cuff can be pinched against the back side of the joint socket as the arm is raised overhead.
A more serious injury to the labrum can also be a result of instability. The labrum is a thick piece of tissue that expands or deepens the “tee” of the shoulder joint allowing for more connection to the arm bone. Similar to placing a heavy block under a car’s tire when parking on a hill to keep it from rolling away, the labrum acts as another passive restraint to help stabilize the shoulder joint.13
The labrum works with the joint capsule to create an airtight seal over the joint. However, if sufficient dynamic stability is not maintained in the joint, excessive motion can occur creating trauma to the labrum and eventual tearing. When the labrum is torn (even slightly) it results in a dramatic drop of pressure inside the joint and a huge loss in passive joint stability. The most common complaints of those who have this type of injury is of painful “catching” or “popping” of the shoulder when trying to move the arm overhead.14
Poor Movement and Technique
The last cause of injury should come as no surprise. When you move poorly, especially when under a load, you increase risk for injury. The most common technique flaws that leads to shoulder pain when lifting occur when the barbell is pushed or held overhead (such as with the snatch, jerk/press or overhead squat). Let’s quickly break down how this happens.
In order for the shoulder joint to remain safe during the snatch or overhead squat, we ideally want to see the the wrists, elbows, shoulders/shoulder blades and extended upper back (thoracic spine) in a vertically stacked alignment. This allows the barbell to be positioned directly over the back of the neck. With the barbell in this location, the shoulder muscles can work efficiently to stabilize the tremendous amount of weight overhead. If all of these factors are aligned properly, you should be able to sit in the bottom of a deep squat and press the bar vertically to the overhead position and back down to the tops of your traps moving only the arms and keeping the rest of the body still.
In order to maintain stability during the entirety of a workout with overhead lifting (such as snatches) the athlete must ensure proper position of the shoulder blades. For most, the scapulas should be slightly retracted (pulled together) but not shrugged upward.
It is a common misconception that a lifter should shrug their shoulder blades upward when the barbell is overhead. Some lifters will appear to have done so as they secure the barbell in the overhead position for two reasons. First the shoulder blades naturally have to upwardly rotate in order to provide stability for the humerus. Second, the upper traps are engaged to help provide tension for the arm as it supports the barbell overhead. The appearance of an upwardly rotated shoulder blade and engaged upper traps gives some the impression that the lifter is actively shrugging their shoulders upward. However, this is often not the case. Excessive upward shrugging of the shoulders can lead to early fatigue of the supporting musculature that stabilizes the joint. Simply put, overemphasizing a shoulder shrug is an inefficient approach to stabilizing the barbell overhead.
Olympian Chad Vaughn explains this concept by telling his athletes to envision doing a 100-meter overhead walking lunge with a barbell over their head. If the shoulders are shrugged upwards to support the barbell, the trap muscles will surely fatigue before the 100-meter distance is covered. The movement foundation for long term support and stability during such a task is the same as the strong and stable position we need for short duration movements like a snatch or a three repetition overhead squat.
One of the most common technique flaws behind shoulder injuries when lifting overhead is when excessive internal or external rotation of the joint occurs. As you raise your arm (or toss a barbell over your head) the shoulder joint moves into slight external rotation to keep the “ball” centered on the “tee”. Because the hands are firmly attached to the barbell, the only way to create more rotation either way is to move the shoulder blades (and therefore the barbell) out of the ideal stacked position. This is when injury occurs.
For example, poor technique can shift the shoulder into excessive rotation in order to keep the body (and the weight overhead) in balance. If the athlete drops their chest forward during an overhead squat the arm will reflexively move further behind the head to keep the barbell balanced over the mid foot. This exaggerated position places the shoulder in a ton of external rotation and shifts the humerus excessively forward in the joint. Lifting weights overhead in this unbalanced position (out of the ideal stacked alignment) places tiny amounts of micro trauma on the small structures of the shoulder and can lead to eventual pain.
(As a side note, I hear a lot of people ask about certain coaches giving the cue to internally rotate the shoulder in the overhead position. I think this is a misunderstanding of the shoulder mechanics. I believe the problem lies in the appearance some athletes give as they squeeze their shoulder blades together and push their armpits forward with the barbell overhead (scapular retraction). While this may appear like the shoulder is moving into internal rotation, the humerus itself is remaining externally rotated in order to stay in the middle of the shoulder blade socket).
Regardless of what cues your coach may give, the basic criteria of maintaining the upper body in a balanced stacked alignment must be met for the shoulder to remain safe when lifting overhead. There will always be a little variation in how the overhand position looks from athlete to athlete due to anatomy (it should come as no surprise that we’re all built a little differently!). However, the foundation for safety and stability when lifting is something we all must adhere to if we want to keep our shoulders safe in the long run.
Keep Your Head Up
By now you should be noticing a common trend in how shoulder injuries occur. Safe and efficient movement is the combined action of both mobility and stability. When either is lacking during the lifts we perform in the weight room, the body slowly sustains harmful micro-trauma that can over time lead to a big injury.
If shoulder pain is something you are currently dealing with, keep your head up. Next week we’ll start the next step towards fixing your injury by teaching you how to properly screen your shoulder.
Until next time,
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