In sports that rely on overhead movements, orthopedic problems of the shoulders can cause disruption of normal athletic movements. Whether you’re a tennis player, Crossfit  athlete, baseball pitcher, competitive swimmer or a Navy SEAL candidate; proper overhead mechanics are essential.

One of the joints that are key to success in activities involving overhead movement and strength is the shoulder. The shoulder joint complex is made up 4 joints that interact with each other during shoulder motion such as abduction, flexion, extension and both internal and external rotation.

The shoulder complex (aka shoulder girdle) consists of the sternoclavicular (SC), acromioclavicular(AC),  glenohumeral(GH) and scapulothoracic joints(ST).  Each one of these joints has a role to play as the arm is elevated overhead.


During abduction and flexion kinematics, the SC joint must perform a posterior roll of the clavicle at the sternum, the AC joint must be able to slide apart from each other (slight separation between the acromion and the clavicle), the GH joint must be able to roll and glide in opposite directions at the glenoid (shoulder socket), and the ST joint must be able to upwardly rotate on the thorax.

In order for the shoulder to produce normal motion of overhead elevation; the relationship between the GH and ST joints is very crucial. During elevation of the arm, there must be a 2:1 ratio between the GH and ST joint1,.  This is known as normal scapulohumeral rhythm.

The GH joint must be able to move 120 degrees of elevation (abduction and flexion) and the ST joint must be able to upwardly rotate the scapula an additional 60 degrees. This equates to the full 180 degrees of motion of the shoulder in these 2 planes. Most shoulder impingements occur at the GH joint, but other joints such as the ST joint play an integral part in the impingement.

What is shoulder impingement?

In shoulder impingement, the tendons of the rotator cuff become squeezed between bones and ligaments.  The most common site of shoulder impingement is in the subacromial  space.  This space is located between the acromion of the scapula (shoulder blade) and the top of the humeral head (shoulder bone).

It is within this space that the tendon of the supraspinatus runs through to its attachment on the humerus bone. During normal elevation of the arm(mainly abduction), the subacromial space needs to have adequate “room” for the tendon of the supraspinatus to slide.

If this space is decreased, the tendon will become caught between these two bones and will not be able to slide appropriately. As a result of the pinching of this tendon, the tendon may become inflamed and cause pain during elevation of the arm.

The supraspinatus tendon is the most common tendon to be impinged. Other structures can also be involved in impingement. Structures such as the subacromial bursa can be implicated as well.  The bursa is located in the same vicinity as the tendon of the supraspinatus.

The bursa acts like a lubricant for the tendon of the supraspinatus to slide normally without difficulty.  The bursa can be inflamed along with the tendon of the supraspinatus3.

People that experience pain from shoulder impingement will feel the pain between 70-120 degrees of upward elevation of shoulder motion. This is known as the painful arch of the shoulder. This is a common sign that should alert you of shoulder impingement.

Since shoulder impingement is synonymous with overuse injuries; it is vital to find and correct the cause of the shoulder impingement.  The inflammation of the tendon and bursa will continue as the activity is repeated over and over again.

This tendinitis of the soft tissue will continue until the arm can no longer be used, the activity needs to stop or the tendon breaks down and eventually ruptures1,2,4.  This condition can seriously affect your upper extremity activity level in both sports and activities of daily living(ADLs).

Shoulder impingement causes

Shoulder impingement is primarily caused by faulty biomechanics of the shoulder1,3,4,5.  The position of scapula, humerus, and the proper resting length of muscles surrounding both the GH and ST will affect the degree of shoulder impingement.

Shoulder impingement_2

The GH joint is the most mobile joint in the body.  The joint has 3 degrees of freedom(moving in all 3 planes of motion: sagittal, frontal and transverse) and has many motions it can perform.

These motions are flexion, extension, abduction, adduction, internal rotation, external rotation, horizontal abduction and horizontal adduction. Due to the many motions the shoulder is free to move in, the joint sacrifices stability.

The ligaments and capsule of the shoulder do a poor job at providing stability.  Therefore, the GH joint relies on dynamic stabilizers to keep the joint stable.  The dynamic stabilizers are the rotator cuff muscles.  These muscles will affect the GH joint and create proper alignment of the humeral head against the glenoid cavity of the scapula.

The rotator cuff muscles are the supraspinatus, infraspinatus, teres minor, and subscapularis.  These muscles must be in the proper resting length to each other in order to stabilize the humeral head and support proper movement.  If these muscles become weak, the humeral head’s alignment will change.

A common misalignment the humeral head makes is a superior translation towards the acromion1,4.  The acromion is located on the scapula and is the most superior projection of this bone. The acromion forms the roof of the subacromial space.  When the humeral head translates toward the acromion, the subacromial space will decrease.

This will encroach the space and create the squeezing of the supraspinatus tendon and/or the subacromial bursa1,2,4.  The superior translation can be affected by a tight trapezium.  The upper trapezium muscles attaches to the spine of the scapula and affects the kinematics of shoulder motion1.

Another misalignment of the shoulder is a anterior translation of the humeral head toward the chest.  This misalignment can be caused by a tight pectoralis major and latissimus dorsi muscles. When these 2 muscles become tight, they will cause a phenomenon known as rounded shoulders.

Rounding of the shoulders will increase anterior translations and contribute to shoulder impingement. Proper alignment of the humeral head is crucial to avoid shoulder impingement.

The other joint that is involved in shoulder impingement is the ST joint.  This joint is actually known as a “false joint” because there are no ligaments or a capsule that make up the joint.

As with the GH joint, the ST joint relies on muscles to stabilize and mobilize the joint. The motions of the scapula bone moving on the thorax are protraction and retraction, upward and downward rotation and anterior and posterior tilting1.

The muscles that produce these motions are the serratus anterior , rhomboids(major and minor),  the trapezium (upper, middle, and lower), and pectoralis minor. These muscles need to be in the their proper resting length in order to be functional to provide these movements during GH elevation.

4 motions that are critical to the proper motion of the scapula are upward rotation, downward rotation and anterior and posterior tilting. In proper scapulohumeral rhythm,  the scapula must upwardly rotate and posterior tilt during the last 60 degrees of shoulder girdle motion1,4.

The GH joint must complete its 120 degrees prior to activation of the scapula1. The serratus anterior, lower  and middle trapezium are key muscles during shoulder girdle elevation1.  If the upper trapezium is tight and overactive then upward rotation will be affected.  If the muscles such as the serratus anterior, middle and lower trapezium are weak and inhibited, the scapula will not be able to upwardly rotate and posterior tilt during flexion or abduction.  As a result, the upper trapezium and pectoralis minor will superiorly translate and anterior tilt the scapula1.

This will result in the scapula moving before the GH joint completes its 120 degree elevation.  When the scapula moves before or during  the GH joint movement, it is known as dyskinesia.  In shoulder kinematics; dyskinesia is the disruption of normal scapulohumeral rhythm4.

Dyskinesia  of the scapula will result in an anterior tilt of the scapula around the head of the humerus and a increased clavicular elevation (from upper trapezium’s attachments on the clavicle)1,4.  As a result of dyskinesia of the scapula on the shoulder girdle, changes in motor control will take place1.

Due to the lack of recruitment from the serratus anterior and lower and middles trapezium, the scapula muscles will activate at the wrong time. Motor control is altered as a result of improper muscular activation of the upper traps and pectoralis minor superseding the appropriate activation of the proper muscles (serratus anterior, middle and lower traps) for normal motion during scapulohumeral rhythm1.

If these biomechanics, recruitment patterns and dysfunctional muscles are not restored and corrected; shoulder impingement will continue and could cause tendinitis, bursitis, degeneration , partial tearing and full rupture of the supraspinatus tendon.

Fortunately, there are things that can be done to remedy shoulder impingement.  A strength and conditioning and flexibility program can help reduce shoulder impingement and return normal biomechanics to the shoulder girdle.

It is important that the athlete understands  the exercises summarized in this article and executes them properly and consistently if they hope to return to a normal healthy functioning kinematically sound shoulder complex.


1.  Phadke V, Camargo PR, Ludewig PM.  Scapular and Rotator Cuff Muscle Activity during Arm Elevation;A Review of Normal Function and Alterations with Shoulder Impingement. Rev Bras Fisioter.2009; 13(1):1-9.

2.  Lawrence RL, Braman JP, Staker JL, Laprade RF, Ludewig PM.  Comparison of 3-Dimensional Shoulder                             

Complex Kinematics in Individuals with and without Shoulder Pain, Part 2: Glenohumeral Joint.  JOSPT. 2014; 44(9):646-655.

3.  Tyson A. Prevention and Rehabilitation of Shoulder Impingement. Strength & Cond. 1995; 17(1): 31- 34.

4.  Allegrucci M, Whitney SL, Irrgang JJ. Clinical Implications of Secondary Impingement of the Shoulderin Freestyle Swimmers. JOSPT. 1994; 20(6): 307-318.

5.  Pabian PS, Kolber MJ, McCarthy JP. Post-rehabilitation Strength and Conditioning of the Shoulder: An Interdisciplinary Approach. Strength & Cond. 2011; 3

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