Like any other joint in the body, the stability of the shoulder joint depends on static and dynamic stabilizers. However, due to the wide range of motion of the shoulder complex (the most flexible joint in the human body), dynamic stabilizers are essential for strong neuromuscular sensation Control all movements and activities involving the upper body.
In this context, neuromuscular control can be understood as “the involuntary activation of dynamic constraints that occur in preparation for and in response to joint motion and loading in order to maintain functional joint stability.”  Dynamic constraints are derived from Promotes neuromuscular control of the shoulder muscles through motor control and proprioceptive input.
Furthermore, the term sensorimotor system describes the sensorimotor and central integration and processing components involved in maintaining joint homeostasis during body movement – often understood as functional joint stability. 
Finally, proprioception in this context can be understood as an important part of the sensorimotor system; thus, the neuromuscular interaction between the receptors of the scapular ligament and the central nervous system ensures mobility and stability of the glenohumeral (GH) joint balance between sex System (CNS) and stabilizing muscles of the shoulder complex. 
Static stabilizers include the joint labrum and parts of the capsuloligements of the glenohumeral joint and the fascia muscles of the entire shoulder. There is also a hypothesis that the neuromuscular bundle (muscle fibers) may also contribute to static static stability.
Dynamic stabilizers include contracting muscles of the stiff shoulder (tendon muscles and tendon-muscular junctions). The best known is the rotator cuff muscles (supraspinatus infraspinatus subscapularis Teres minor) which together control the fine movements of the humeral head in the glenoid fossa (hold the humeral head midway during stability and movement). In addition, the periscapsular muscles which are very important for shoulder integrity while avoiding biomechanical misalignments such as the shoulder impingement impingement.
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The stability of the stiff shoulder can be categorized into:
- Glenohumeral stability (Local)
- Scapulothoracic stability (Global)
Check out the Physiopedia page on Biomechanics of the Shoulder for an in-depth analysis of the connections and contributions of global motion and the fine musculature of the strong shoulder.
Glenohumeral joint stability
The deltoid muscle plays an important role as a stabilizer and is generally recognized as a major trigger for the glenohumeral joint when abducted along with the supraspinatus muscle.
The deltoid is the main muscle for abduction of the forearm from 15 to 90 degrees.It is also the primary stabilizer of the humeral head in cases of weight bearing.
From the biomechanical diagram, the upwardly directed component (fx) of the parallel force of the active element (line of pull) of the deltoid with its arm next to the body is the largest of the other three segments; resulting in the use of superior and minimal translation of the humeral head extensive forces are transmitted to the rotation of the lungs. There is also a low force pull (fx) to activate the middle deltoid component as the arm is raised because gravity is not balanced solely with respect to the force surrounding the GH joint . . . .
figure 1 line of action of three parts of deltoid follows line of pull of middle deltoid deltoid force readied into a very large translational component (Fx) and a small rotational component (Fy).
Blood supply to the deltoid: The posterior circumflex humeral artery and the deltoid branch of the thoracoacromial artery are the arteries that supply the deltoid.
Nerve of the deltoid: The nerve supplying the deltoid passes through the axillary nerve (C5 C6) from the posterior cord of the brachial plexus.
Rotator Cuff muscles
The rotator cuff (RC) (collectively the following muscles: supraspinatus subscapularis infraspinatus teres minor) not only arrests the shoulder but also plays an important role as a stabilizer. The primary role of the rotator cuff is to control the correct (small) movement of the head the humerus of the glenoid fossa (usually thought to be connective tissue). The rotator cuff muscles help keep the femoral head centered during stability and dynamic movement. This is extremely important in terms of neuromuscular control because it helps to avoid a biomechanical impingement of the soft tissues below the subacromial arch during elevation movements.
From Figure 2, three of the RC muscles (teres minor subscapularis infraspinatus) can be seen with respect to their anatomic position and the orientation of their muscle fibers from origin to insertion. This is important to note since similar low pull rates and combinations are often obtained the three force vectors of the rotator cuff were virtually counteracted by the superior translation of the humeral head induced by the deltoid muscle.
Also the extensional motion of the shoulder is allowed by the periods of rotation of the cuff muscles. The teres minor and infraspinatus muscles form external rotators and are involved in reduction of the large muscle beneath the acromion during shoulder movement.
The supraspinatus arrested the shoulder from (0-15) and has an effective role as a shoulder stabilizer by keeping the humeral head pressed medially over the glenoid cavity this strengthening function enables the supraspinatus and deltoid support at the shoulder they are captured and kept.
Regarding the location of the supraspinatus muscle, it is superior to the other three rotator cuff muscles. It therefore has the highest pull without counteracting the force from the deltoid muscle.
From Figures 1 and 2 we can consider the deltoid and rotator cuff muscles as a combined cumulative force for motion associated with the glenohumeral joint.
Imbalances in one or more of these muscles can cause biomechanical misalignments and contribute to shoulder dysfunction such as: impingement disorders bursitis instbilities scapular dyskinesia or chronic conditions associated with pathological wear and tear.
Supraspinatus blood supply: the suprascapular artery supplies blood to the supraspinatus muscle.
Innervation of the supraspinatus: The supraspinatus is innervated by the suprascapular nerve (C5 C6) from the upper pole of the brachial plexus.
Scapulothoracic joint stability
Because the scapulothoracic joint is a floating joint it relies solely on neuromuscular control (proper strength and control of the stabilizer muscles as well as a proper sense of muscle timing). Agonist antagonist and synergist neurotransmission is essential for a normal and non-inflammatory response scapulothoracic rhythm. For movement during elevation and reaching operations it is important to consider the force-coupling acting on the floating joint. Such muscles to consider are serratus anterior serratus posterior trapezius (upper / middle / lower) rhomboids teres major the levator scapulae latissimus dorsi and the flexibility and mobility of the thoracolumbar fascia.
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Serratus anterior (SA)
During reaching or functional activities that require the lengthening of the upper arm your scapula will be delayed and elevated which is mainly caused by the serratus anterior ms. As movement of the scapulothoracic occurs in response to the AC overlap and SC joints. SA creates this movement by acting on the scapula It can maintain scapulothoracic upward rotation throughout the arm height and also contributes to external rotation and post tilting of the scapula. The lower SA fiber has a moment arm long enough to hold this together scapular upward rotation.
Lowe trapezius muscles help SA to upward rotation of scapula which helps to maintain subacromial space.
A strong serratus action as a protractor/upward rotator needs an adequate force to control this movement (an equally strong antagonist). The serratus anterior and trapezius (middle) muscles act as the primary coupling force for upward rotation of the scapula.
Blood supply to the serratus anterior: the posterior aspect of the anterior portion of the upper thoracic artery and the inferior portion of the thoracodorsal artery
Innervation of the serratus anterior: long pulmonary nerves C5-C7 from the brachial plexus
It is a broad superficial muscle which is divided into a median and lateral portion each part has a different fiber direction that is why it has different actions. The upper part fits into the clavicle and has no attachment to the middle of the scapula attached to the acromion and spine of the scapula and the lower part inserts into the medial base of the scapular spine.
It is most active when the arm is raised in abduction and there is a gradual linear increase in activity as the angle of abduction increases.
Upper trapezius: so the scapulothoracic movement occurs in response to the combined movement of the AC and SC joints and the upper trapezius attaches to the clavicle it has a mild indirect effect on scapular upward rotation and a strong effect on scapular external rotation on. When it contracts with it a stable craniocervical region causes the clavicle to move upward and backward at the level of the sternoclavicular joint. Clavicle retraction contributes to 100% of the scapular external and clavicle elevation contributes approximately 75% of the scapular anterior tilt and 25% of the scapular upward rotation of the weakness of the scapula.
Middle and lower ligaments: they assist with the serratus anterior to rotate the scapula upward after rotation of the scapula through their torque on the AC joint and have a retractor force on the scapula with force preventing the extension of the SA muscle
Lower trapezius: together with the serratus anterior muscle performs the main upward rotation of the scapula. It helps in upward rotation of the scapular when the axis of elevation reaches the acromioclavicular joint.
Middle trapezius: has a downward and upward moment arm arising from the scapula. Its downward arm moment is stronger (greater moment arm) than upward moment on the scapula in addition to its withdrawal force helps to offset the strong action of the serratus anterior as a protractor and upward rotator (acts as an antagonist) .
The serratus anterior and trapezius muscles act as agnostics for increased scapular rotation. and prevent the downward rotational motion caused by the deltoid (medial/external) and muscles are produced in conjunction with the deltoid in connection with the glenohumeral forces that arrest the G.H joint.
This movement is associated with downward rotation of the scapula and internal rotation of the shoulders and sinking of the shoulders as the shoulders are extended or brought back to the side of the body.
Latissimus Doris, Pectoralis major.
The latissimus dorsi is a muscle in the back that attaches to the scapula and humerus. The pectoralis major is a superficial muscle in the pectoral region, with sternum and clavicle portions. The lats help to adduct and depress the scapula and shoulder complex in conjunction with the pectoralis major The specialty of shoulder adduction.
They act as a stabilizer when the arm is raised; the latissimus dorsi acts on the G.H joint pectoralis major through its compressive force through a higher reaction force.
It connects to the coracoid process and thus helps to rotate the scapula downward, internally, and anteriorly. And it cooperates with the latissimus dorsi and pectoralis major muscles to adduct and internally rotate the shoulder joint, which has the effect of adducting and internally rotating. shoulder rotation
Rhomboids and teres major muscles
The teres major has the same adduction, extension, and internal rotation actions as the latissimus dorsi. Since it attaches to the scapula at the proximal humerus for effective adduction and extension, it pulls the humerus to the scapula (stabilizing part), so this movement is relative to the downward movement of the scapula Rotate and retract.
The function of the teres major depends on the activity of the rhomboids because it stabilizes the scapula on the chest wall to rotate the scapula downward during adduction and extension of the GH joint, without sufficient stabilization the teres major will rotate upwards rather than downwards.
Additionally the rhomboid muscles work intricately to regulate changes in the position of the scapula when the arm is raised. Thus it acts as an antagonist to the external translational force of the serratus anterior muscle.
For a stable shoulder to move properly, we need the combined forces of the glenohumeral and scapulothoracic joints to act in synchrony and with adequate mutual resistance tip.
For example; the deltoid muscles (specifically the medial fibers) act to stabilize the humeral head against the glenoid as the arm is raised, while the rotator cuff muscles (specifically the subscapularis teres minor infraspinatus) control the fine-tuned movement of the humeral head.
These strength deficiencies, such as rotator cuff/deltoid underactivation or muscle overactivation, lead to narrowing of the subacromial space (Figure 3). This can compress the tendons and soft tissues within this space, causing acute or chronic inflammation and dysfunction (rotator cuff tendinopathy/shoulder impingement) .
Winged scapula and scapular dyskinesia may also occur due to an imbalance of the scapular muscles. For example; serratus anterior and lower trapezius weakness and/or upper trapezius overactivation Prolonged overactivity of the inferior rotator can affect The scapula is rotated upward, and the forward tilt of the scapula can be seen. and adaptive shortening of the pectoralis minor . This alters the dominant tension line of the scapula during movement and can lead to pathological movement patterns.
Physical therapy interventions
Rehabilitation should focus on restoring normal biomechanical alignment of the shoulder complex (centralization of the GH joint, correct scapular glide of the scapula) and restoring proper force coupling balance of the stabilizing muscles.
Proper strengthening of the shoulder dynamic stabilizers and proper neuromuscular control patterns are critical for rehabilitation and prevention of shoulder injuries.  
Under the direction of a supervising physical therapist, neuromuscular exercises usually focus on quality of movement. Neuromuscular exercises often include strength coordination balance and proprioceptive components. [twenty one]
Exercises can be performed unilaterally or bilaterally in unstable conditions, including improving postural control (standing plank and lying on a stability ball) and/or using external overloading devices that challenge motor coordination (bouncy ball dumbbells). [twenty two]
Resistance training can promote neural and structural changes in the shoulder complex  and can increase sensory biomechanics and motor processing patterns  (e.g. cervicothoracic shoulder complex and upper extremity as a whole).
Kinetic chain exercises of the lower extremity and trunk during shoulder rehabilitation can reduce demands on the rotator cuff and improve recruitment of the axial scapular muscles .
Overall, to restore neuromuscular control of the shoulder complex, the therapist should focus on the following elements:
- Full and pain-free range of motion for the cervical and thoracic spine.
- There were no neurologic signs or symptoms in the cervical spine throughout the upper extremities.
- Full and pain-free range of motion for all distal joints (fingers thumb wrist elbow).
- Postural control under static and dynamic conditions (neutral spinal concentration with correct scapular setting of GH joint).
- Proper biomechanical alignment and accessory movements of 4 shoulder rigid joints (GH joint acromioclavicular joint sternoclavicular joint and floating scapulothoracic joint). It is also wise to check the accuracy of all the lung movements and breathing patterns.
- Tightness of common muscle weakness / obstruction (Such as the serratus anterior rotator cuff muscle of the lower trapezius rhomboid muscle) .
- The presence of muscle rigidity due to postural stress and excessive muscle activity (such as the presence of stimulus sites).
- Stiffness and immobility of the surrounding fascia or fascial rail.
- Lack of mobility in upper extremity neck and thoracic neural tissue (neural flossing as needed).
- Tension in any static tissue such as GH capsules.
- Acute stretching of the muscles that are often shortened and possibly overworked (Pectorals muscles upper trapezius levator scapulae muscles) .
- Reeducation of the rotator cuff muscles (working in rotations at different angles of elevation scaption movement and functional activities).
- Eccentric exercises for the rotator cuff muscles in case of suspected rotator cuff tendinopathy to restore collagen assembly in the muscles.
- Strength of the surrounding supporting muscles (Biceps triceps latissimus dorsi rhomboids muscles that stabilize the cervix posterior spinal support muscles).
- Muscle re-education of agonist-antagonist and synergist muscles. Muscle timing (coordinated contraction) is a key component to focus on during shoulder rehabilitation.
Progression factors to consider for challenging neuromuscular control of the shoulder complex:
- Posture control and localization: Static pose to dynamic motion.
- Strengthening: body weight/rehab belts/free weights/functional strengthening.
- Repetition: endurance (high repetitions low load) strength and performance (low repetitions high load).
- Speed: slow to move fast (always under control).
- Joint loading: not a weight-bearing load.
- Floor: rigid surface (wall / floor) to unstable surface (bosu ball stability disc movement boards) also incline vs. surface. decline.
- Joint mobility: Single joint motion (i.e. GH joint only) to multijoint motion (total and upper extremity shoulder).
- Functional movements: shot catching rolling and sport specific movements. Also external disturbances such as the use of Water Pipes (training devices containing sand or water to cause reactionary movements).
More exercises for the rotator cuff complex:
- Choosing Exercises – Rotator Cuff Related Shoulder Pain Interview with hilkka virtapohja
- Systematic review: Exercise rehabilitation for rotator cuff tears (2016)
For related topics:
- Neuromuscular exercise program
- Neuromuscular adaptations to exercise
- Shoulder instability
- Motor control
- Biomechanics of the shoulder
- Throwing biomechanics
Check out some more resources:
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