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Many common resistance-training exercises designed to isolate specific muscles don’t account for the separate skeletal structures and how they are designed to move as a single unit. In this fourth installment of our functional anatomy series, we examine the integrated actions of the four joints that make up the shoulder complex. Specifically, you’ll learn how the separate joints are designed to function as an integrated unit and the common exercises that could be causing injuries. Also highlighted are strategies for improving the stability, mobility and strength of this oft-injured body part.
The skeletal system of the body is organized into two different components: the axial skeleton, which is comprised of the spine, skull and rib cage, and the appendicular skeleton, which includes the pelvis, legs, shoulders and arms. The shoulder is composed of four distinct joints and is the foundation of movement for the arms:
The ball-and-socket structure of the GH joint allows a significant range of motion in all three planes. The ST and SC joints allow motion primarily in the frontal and transverse planes, while the AC joint allows only a limited amount of motion, which is critical for the optimal function of the other joints (Table 1). Individually, each of these joints allows a specific range of motion, but when functioning as an entire unit the shoulder becomes one of the most mobile parts of the human body. The paradox of the shoulder complex is that it needs to have the stability required to prevent unwanted motion, while also having the mobility necessary for many dynamic movements. When even one of these four joints is out of alignment, it can interfere with how the others function—reducing the shoulder’s ability to move freely or remain stable as needed.
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Table 1. Joints and Motions of the Shoulder |
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Joint |
Bones |
Sagittal Plane Motion |
Frontal Plane Motion |
Transverse Plane Motion |
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Sternoclavicular (SC) |
Sternum First rib Clavicle |
When the shoulder flexes or extends in the sagittal plane, the clavicle will spin anteriorly and posteriorly, respectively. |
Elevation Depression |
Protraction Retraction |
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Acromioclavicular (AC) |
Clavicle Scapula - acromion process |
“Measuring isolated motions at the AC joint is difficult and is not done in typical clinical situations.” (Neumann, 2010) |
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Scapulothoracic (ST) |
Scapula Posterior rib cage |
N/A |
Elevation Depression Upward rotation Downward rotation |
Protraction Retraction |
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Glenohumeral (GH) |
Scapula - glenoid fossa Head of humerus |
Flexion Extension |
Abduction Adduction |
Internal rotation External rotation |
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Effective exercises for a healthy, asymptomatic shoulder should focus on movements that incorporate motion of all four joints at the same time. |
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The shoulder can move in all three planes of motion—sagittal, frontal and transverse—and many common exercises focus on movement of the shoulder in one of these planes at a time. However, when selecting exercises to enhance shoulder strength, it is important to consider that there is a fourth plane of motion created by the way the glenoid fossa of the scapula sits relative to the thoracic rib cage. In a healthy shoulder, the concave socket of the glenoid fossa points in an angle that is approximately 35 degrees anterior to the frontal plane. This fourth plane of motion is often overlooked in many shoulder exercises, which could potentially be a cause of many injuries. The position of the glenoid fossa means that overhead movements should be neither wholly in the sagittal plane nor in the frontal plane, but should be somewhere in the middle, where the elbows are pointing approximately 30 to 45 degrees from the center front of the body (at about the 10 o’clock and 2 o’clock positions). This position is referred to as the scapular plane.
The term “elevation” is used to describe movement of the arm overhead without identifying the specific plane of motion. Movement of the arm into the overhead position is produced by muscles that can be organized into three groups:
As the arm is elevated above the height of the shoulder, the glenoid fossa should move under the head of the humerus to support the weight of the arm (and whatever it might be holding) as it extends overhead; the technical term for this is scapulohumeral rhythm. In a healthy shoulder, as the deltoids contract to move the humerus overhead in the scapular plane, the muscles of the rotator cuff, specifically the supraspinatus, infraspinatus, teres minor and subscapularis, pull the head of the humerus into the glenoid fossa to create stability as the arm moves into the fully extended, overhead position. In an injury-free shoulder, there should be a 2:1 ratio of movement of the humerus to the scapula. As the humerus moves to a position where it is 120 degrees relative to the body, the scapula will upwardly rotate (the point of reference is the glenoid fossa) up to 60 degrees to support the arm.
Shoulder presses done in the frontal plane, with the elbows pointed at 9 and 3 o’clock, could cause an injury to specific shoulder muscles. When the humerus is held in an externally rotated position to perform an overhead press in the frontal plane, the deltoid tuberosity can impinge the long head of the biceps brachii and the supraspinatus muscle between the coracoid and acromion processes, respectively. In addition, as the supraspinatus is compressed between the humerus and acromion process, it changes the length-tension relationships of the other rotator cuff muscles, which can inhibit their ability to effectively stabilize the humerus when the arm is extended overhead.
Try this: Hold your arms out in the frontal plane and perform a few overhead presses. You should feel a slight impingement about 75 to 80% of the way through the motion. Now move your arms to the mid-way point between the sagittal and frontal planes and try a few presses. You should feel how your arm can extend all of the way overhead without any restriction. With the arm overhead in the scapular plane, the serratus anterior, lower trapezius and upper trapezius are in an optimal position to stabilize the ST joint, which is a much safer way to perform overhead presses.
Performing front raises while holding the hands in a palms-down, pronated position creates internal rotation at the GH joint, which can reduce space in the anterior compartment of the joint impinging the long head of the biceps brachii. A more effective way to strengthen the anterior deltoids is to hold the hands in a neutral position with the palms facing the midline of the body or to perform V-raises (see the workout for shoulders below).
During normal movements, muscles contract as a reflex to provide the force required to either stabilize a joint to prevent unnecessary motion or to cause a specific segment of the body to move. Whether the function is to provide stability or initiate motion, an essential component of a muscle’s ability to function properly is its resting length. If a muscle is held in either a shortened or lengthened position for an extended period of time, its ability to function properly will be altered. When the resting length of a muscle changes, both the position of the bones to which it’s attached as well as the structure of the joints where it influences motion will be changed.
Many people have poor upper-body posture, with shoulders that are slumped and rounded forward. This can drastically change the length-tension relationships of the muscles; specifically, the second group of muscles that control upward rotation of the scapula (trapezius, levator scapulae, rhomboids and serratus anterior) and are responsible for moving and stabilizing the scapula to maintain optimal glenohumeral rhythm. So, does a change in muscle length change the alignment of a joint or does a misalignment of a joint change the length of involved muscles? “It’s not exactly clear,” says Gray Cook, a physical therapist and creator of the Functional Movement Screen, “but what we do know is that poor posture or alignment changes the information relayed to the central nervous system, which can inhibit muscle activity.
What is important,” Cook continues, “is to first strengthen the muscles responsible for stabilizing shoulders before focusing on the muscles that create movement at the joints.”
All of the muscles responsible for stabilizing and moving the shoulder should be trained in a way that improves their ability to function, allowing the scapula and humerus to move together as a single integrated unit. The anterior, medial and posterior heads of the deltoid help abduct the humerus away from the midline of the body and are some of the most visible muscles of the shoulder complex. As a result, the traditional overhead press focuses the movement in the frontal plane in an effort to maximize the recruitment of these muscles. However, successful, pain-free overhead movements with the shoulder rely on the deeper muscles of the rhomboids, serratus anterior and levator scapulae, as well as the superficial trapezius, to work together to move and stabilize the scapula to create a stable foundation as the arm is raised overhead.
The deltoids will generate the force to move the humerus; however, the scapular stabilizers are responsible for moving the cup of the glenoid fossa as the rotator cuff muscles hold the head of the humerus stable in the joint (with the joint surface of the glenoid fossa pointed 30 degrees anterior of the frontal plane). As the arm moves overhead and the scapula rotates upward to support the weight of the limb, the muscles of the rotator cuff—the supraspinatus, infraspinatus, teres minor and subscapularis—work to pull the head of the humerus into the glenoid fossa. Rounded, protracted shoulders can change the length-tension relationship of all these muscles, which will significantly alter how the joint functions when the arm is raised, especially if the elbows are held in the frontal plane, as they are during traditional overhead presses. If the muscles of the shoulder cannot properly stabilize the scapula and control motion of the humerus to create optimal scapulohumeral rhythm as the arm moves above shoulder height, impingement could occur and be a potential mechanism for injury. Effective exercise program design for the shoulder should first create stability of the ST joint, restore the length-tension relationships of the muscles responsible for controlling the scapula and finally generate the force to both create stability of the GH joint and move the arm overhead (Table 2).
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Table 2. Muscles Responsible for Elevating and Stabilizing the Shoulder |
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Joint |
Muscles |
Movement(s) |
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Glenohumeral |
Anterior and medial deltoid Supraspinatus Coracobrachialis Biceps (long head) |
Elevate the humerus in the sagittal and frontal planes |
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|
Scapulothoracic |
Serratus anterior Trapezius |
Upward rotation of the scapula (moving the surface of the glenoid fossa to face up) and rotation of the scapula around the rib cage (toward the front of the body) |
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|
Rotator cuff |
Supraspinatus Infraspinatus Teres minor Subscapularis |
Provide dynamic stability of the head of the humerus as it slides, spins and rolls against the surface of the glenoid fossa |
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Individual muscles rarely work as isolated units, but often function synergistically with other muscles to create the force necessary for efficient joint motion. In the shoulder, a number of muscles work together to produce opposing forces to generate scapulohumeral rhythm and create the dynamic stability necessary for efficient movement. In a healthy shoulder, the muscles responsible for elevating the humerus initiate motion at the shoulder. The muscles responsible for stabilizing the ST joint will move the scapula under the head of the humerus, while the rotator cuff muscles will pull the humerus into the glenoid fossa to create stability. When the scapula is held in an abnormal position—where the glenoid fossa is not pointing approximately 35 degrees anterior of the frontal plane—it will change the length-tension relationships of the muscles and reduce the ability of the shoulder to remain stable when the arm is overhead. |
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Adapted from Neumann, 2010. |
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The first step in developing strong, functional shoulders is improving the stability of the ST joints and restoring the length-tension relationships of the muscles responsible for moving and stabilizing the scapulae. Isometric muscle activation that maintains consistent force can help improve the strength of the middle and lower trapezius as well as the rhomboids, which is important for creating ST joint stability. Lying supine with the arms raised overhead so that the palms are facing one another can help teach a client how to engage the scapular stabilizers with the humerus in a flexed, overhead position. And the high plank, which is a closed-chain (hands-on-floor) exercise, can help to develop shoulder stability and strengthen the scapular stabilizers and rotator cuff muscles.
Once the initial stabilization is improved, Cook suggests training the entire shoulder complex using exercises that enhance the ability of the muscles to create stability as an automatic reflex. “The muscles responsible for dynamic stability of the scapula and ST joint are reflex dependent,” explains Cook. “When placed in the correct position, the body will know how to create dynamic stability as an automatic response. If your alignment is good and your body position is where it needs to be, your brain will reflexively fire to give the joint necessary integrity.”
Cook’s go-to exercise series for improving the stability and strength of the shoulder is the Six Position Carry, which requires an individual to carry a kettlebell with three specific holds for each arm: the Overhead Carry, the Racked Carry and the Suitcase Carry (see workout below). Cook prefers the kettlebell because it requires a strong grip and the muscles responsible for grip strength have direct “feed-forward neurology” to the muscles responsible for moving and stabilizing the shoulder.
When it comes to helping clients improve their strength, Cook urges trainers to focus on allowing clients to develop the necessary reflexes by using integrated movement patterns rather than isolated motions. “We should coach position,” Cook argues. “If you have to tell somebody to engage their muscles, what is going to happen when they get in a real-world situation and you’re not there to help them execute the pattern?”
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Exercises to Improve Stability, Mobility and Strength of the Shoulder |
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Exercise |
Purpose |
Description |
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Enhance stability of the ST joints; help improve the length-tension relationships and improve the strength of the muscles that stabilize the scapulae |
Lie supine with feet flat on the floor. Extend both arms overhead with the palms facing each other so that the thumbs and arms are resting on the floor. Retract the shoulders and think about pulling the shoulder blades down toward the low back, while pressing the thumbs into the floor. Hold for 15 to 20 seconds, relax for 15 to 20 seconds and repeat four to five times. |
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Enhance stability of the ST joints with the hands in a closed-chain position to provide more proprioceptive input into the shoulder joints |
Press both hands into the floor and push the body up into the shoulder blades while externally rotating each shoulder. Contract the glutes and thighs for additional stability. Hold for 15 to 20 seconds, rest for 30 to 45 seconds and repeat for a total of three to four sets. |
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Gary Cook’s Six-position Carry: Overhead Carry, Racked Carry and Suitcase Carry
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Use proprioceptive feedback to place scapulae in proper position with an extended spine. Holding a weight overhead and carrying a weight laterally initiates a reflex that causes the thoracic spine to extend and the scapula to retract and depress to create stability for the shoulder. |
Overhead Carry: Grip a dumbbell or kettlebell in the right hand and extend it all of the way overhead so that the palm is facing the midline of the body and the elbow is facing forward. Retract the shoulder blade while keeping the arm extended and walk forward approximately 30 steps. Switch hands and return to the starting position with the left arm extended overhead. After completing one overhead carry with each arm, perform a racked carry.
Racked Carry: Hold a kettlebell in a “racked” position so that the scapula is depressed and the humerus is held close to the body with the elbow near the rib cage and the wrist flexed to support the weight. Walk approximately 30 steps, switch hands and return to the starting position. After performing one racked carry with each arm, perform a suitcase carry.
Suitcase Carry: Grip the weight in the right hand so that the palm is facing the thigh with the thumb pointed forward. Walk forward for 30 steps, switch hands and return to the starting position. After completing one trip with each hand for each carry, rest for 30 to 60 seconds and repeat for two to three sets.
(Note: If the grip starts to fatigue, switch hands or rest.) |
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Moving in the scapular plane, which is determined by the angles of the glenoid fossa as the scapulae sit on the rib cage, can help strengthen muscles that stabilize the scapulae as well as improve the mechanics of the GH joint |
Stand with feet hip-width apart. Hold one dumbbell in each hand so that the arms are straight with the weights resting on the thighs and the palms rotated up at a 45-degree angle. Press both feet into the floor, maintain a long spine and raise the right arm up to shoulder height in a 30-degree angle to the front of the body. Slowly lower the right arm. Once the right hand is resting on the right thigh, keep the left arm straight and raise the left hand to shoulder height. Alternate arms, performing 10 to 12 reps on each side. Rest for 60 seconds and complete two to three sets. |
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One-arm Overhead Kettlebell Press
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Train proper scapulohumeral rhythm by focusing on the movement of one arm at a time |
Stand with the feet hip-width apart so that the right foot is slightly in front of the left. Grip a kettlebell with the right hand while holding it in the racked position (the right wrist should be bent with the right elbow held next to the rib cage so the kettlebell is resting on the right forearm). Start the move by pushing the left foot into the floor to shift the weight forward. Press the right arm straight overhead—think about pulling the scapula down toward the lower back. To lower the weight, think about pulling the right elbow back down to the rib cage. Perform four to six repetitions with the right arm before switching to the left. Rest for 60 seconds after using both arms and complete two to three sets. (Note: This exercise may also be performed using a dumbbell.) |
Your role as a health and exercise professional is to help your clients achieve their goals in the safest, most time-efficient manner possible. Understanding how the four joints of the shoulder are designed to work together can help you identify the safest, most effective strategies to help clients improve their upper-body strength. When it comes to designing a workout, the goal should be to help clients develop reflexive strength so they can be successful, even when you aren’t standing right there coaching an exercise. After all, empowering clients to be successful on their own is one of the most important results you can deliver.
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