Anatomy & Stretching 101 Intrinsic Shoulder

Anatomy and Stretching 101

Scapulohumeral (Intrinsic Shoulder) Muscles There are six scapulohumeral muscles: • • • • • •

Deltoid Teres major Supraspinatus Infraspinatus Subscapularis Teres minor

They are relatively short muscles that pass from the scapula to the humerus and act on the glenohumeral joint. These muscles are illustrated and their attachments, nerve supply, and main actions are summarized in Table 1.

Table 1. Scapulohemeral (intrinsic shoulder) muscles Muscle

Proximal Attachment

Distal Attachment

Innervation1

Main Action

Deltoid

Lateral third of clavicle; acromion and spine of scapula

Deltoid tuberosity of humerus

Axillary nerve (C5, C6)

Clavicular (anterior) part: flexes and medially rotates arm Acromial (middle) part: abducts arm Spinal (posterior) part: extends and laterally rotates arm

Supraspinatus2

Supraspinous fossa of scapula

Superior facet of greater tubercle of humerus

Suprascapular nerve (C4, C5, C6)

Initiates and assists deltoid in abduction of arm and acts with rotator cuff muscles2

Teres minor2

Middle part of lateral border of scapula

Inferior facet of greater tubercle of humerus

Axillary nerve (C5, C6)

Laterally rotates arm; acts with rotator cuff muscles2

Subscapularis2

Subscapular fossa (most of anterior surface of scapula)

Lesser tubercle of humerus

Upper and lower subscapular nerves (C5, C6, C7)

Medially rotates arm; as part of rotator cuff, helps hold head of humerus in glenoid cavity

The spinal cord segmental innervation is indicated (e.g., “C5, C6” means that the nerves supplying the deltoid are derived from the fifth and sixth cervical segments of the spinal cord). Numbers in boldface (C5) indicate the main segmental innervation. Damage to one or more of the listed spinal cord segments or to the motor nerve roots arising from them results in paralysis of the muscles concerned.

2 Collectively, the supraspinatus, infraspinatus, teres minor, and subscapularis muscles are referred to as the rotator cuff, of SITS, muscles. Their primary function during all movements of the glenohumeral (shoulder) joint is to hold the humeral head in the glenoid cavity of the scapula.

1

Deltoid • The deltoid is a thick, powerful, coarse-textured muscle covering the shoulder • Forms a rounded contour (Images 1-5).

• As its name indicates the deltoid is shaped like the inverted Greek letter delta (Δ).

• The muscle is divided into unipennate fibers-anterior and posterior parts can act separately or as a whole.

• When all three parts of the deltoid contract simultaneously, the arm is abducted.

• The anterior and posterior parts act like guy ropes to steady the arm as it is abducted.

• To initiate movement during the first 15° of abduction, the deltoid is assisted by the supraspinatus.

• When the arm is fully adducted, the line of pull of the deltoid coincides with the axis of the humerus; thus it pulls directly upward on the bone and cannot initiate or produce abduction (Image A below). The deltoid becomes fully effective as an abductor after the initial 15° of abduction.

IMAGE A

Image A. When the arm is fully adducted, the line of pull of the deltoid coincides with the axis of the humerus; thus it pulls directly upward on the bone and cannot initiate or produce abduction.

It relies upon the supraspinatus to initiate the first 15 degrees of abduction.

• It is, however, able to act as a shunt muscle, resisting inferior displacement of the head of the humerus from the glenoid cavity, as when lifting and carrying suitcases.

• The anterior and posterior parts of the deltoids are used to swing the limbs during walking.

• The anterior part assists the pectoralis major in flexing the arm, and the posterior part assists the latissimus dorsi in extending the arm.

• The deltoid also helps stabilize the glenohumeral joint and hold the head of the humerus in the glenoid cavity during movements of the upper limb.

To test the deltoid (or the function of the axially nerve that supplies it), the arm is abducted, starting from approximately 15°, against resistance (Fig. 6.31). If acting normally, the deltoid can easily be seen and palpated. The influence of gravity is avoided when the person is supine.

IMAGE 1

Image 1. A Deltoid muscle including anterior, medial and posterior heads

IMAGE 2

Image 2. Deltoid muscle including anterior, medial and posterior heads

IMAGE 3

Image 3. Posterior head of deltoid

IMAGE 4

Image 4. Medial head of deltoid

IMAGE 5

Image 5. Anterior head of deltoid

Teres Major • The teres major (L. teres, round) is a thick, rounded muscle passing laterally from the inferolateral third of the scapula.

• The teres major adducts and medially rotates the arm.

• It can also help extend it from the flexed position • is an important stabilizer of the humeral head in the glenoid cavity – that is, it steadies the head in its socket.

IMAGE 6

IMAGE 7

Teres Major • Adducts and medially rotates arm at GH joint • Thick and fusiform in shape • Assist in extension • Referred to as the “little helper” to the lats.

Image 6 & 7. Teres major

Rotator cuff muscles IMAGE 8

Image 8. Posterior view of rotator cuff muscles

IMAGE 9

Image 9. Anterior view

Four of the scapulohumeral muscles (intrinsic shoulder muscles) are called rotator cuff muscles because they form a musculotendinous rotator cuff around the glenohumeral joint referred to as the SITS muscles • Supraspinous • infraspinatus, • teres minor • subscapularis • All except the supraspinatus are rotators of the humerus; the supraspinatus, besides being part of the rotator cuff, initiates and assists the deltoid in the first 15° of abduction of the arm. See Image A above.

• The tendons of the SITS muscles blend with and reinforce the fibrous layer of the joint capsule of the glenohumeral joint, thus forming the rotator cuff that protects the joint and gives it stability.

• The tonic contraction of the contributing muscles holds the relatively large head of the humerus in the small, shallow glenoid cavity of the scapula during arm movements. See Image B.

IMAGE B

Image B. The rotator cuff muscles pull the head of the humerus into the glenoid fossa during dynamic movement. They are sometimes called “dynamic ligaments.”

The rotator cuff muscles and their attachments, nerve supply, and main actions are listed in Table 1.

SEARCH TIP “Fibrous membrane of glenohumeral joint” on your 3D program to see the external layer of the articular capsule of the glenohumeral joint. You will also see the “cuff” that is formed by the rotator muscles around this capsule.

Supraspinatus

IMAGE 10

• The supraspinatus occupies the supraspinous fossa of the scapula. Image 10 • A burse separates it from the lateral quarter of the fossa.

• To test the supraspinatus, abduction of the arm is attempted from the fully adducted position against resistance, while the muscle is palpated superior to the spine of the scapula.

Image 10. Supraspinatus

Infraspinatus.

• The infraspinatus occupies the medial three quarters of the infraspinous fossa and is partly covered by the deltoid and trapezius. Image 11 • In addition to helping stabilize the glenohumeral joint, the infraspinatus is a powerful lateral rotator of the humerus.

• To test the infraspinatus, the person flexes the elbow and adducts the arm. The arm is then laterally rotated against resistance. If acting normally, the muscle can be palpated inferior to the scapular spine.

IMAGE 11

IMAGE 12

Teres Minor • The teres minor is a narrow, elongate muscle that is completely hidden by the deltoid and is often not clearly delineated from the infraspinatus. Image 12 • The teres minor works with the infraspinatus to rotate the arm laterally and assist in its adduction.

• The teres minor is must clearly distinguished from the infraspinatus by its nerve supply. The teres minor is supplied by the axially nerve, whereas the infraspinatus is supplied by the suprascapular nerve (Table 1).

Image 12. Teres minor IMAGE 13

Subscapularis • The subscapularis is a thick, triangular muscle that lies on the costal surface of the scapula and forms part of the posterior wall of the axilla. Image 13.

• It crosses the anterior aspect of the scapulohumeral joint on its way to the humerus.

• The subscapularis is the primary medial rotator of the arm and also adducts it.

Image 13. Subscapualris

• It joins the other rotator cuff muscles in holding the head of the humerus in the glenoid cavity during all movements of the glenohumeral joint (i.e., it helps stabilize this joint during movements of the elbow, wrist, and hand).

Stretching Many of the stretches for the posterior and anterior axioappendicular muscles, and the muscles of the arm will directly affect the intrinsic shoulder muscles. The stretches below may provide a more precise and direct targeting of the region.

Partner Internal Rotators HOW TO STRETCH: Photo A - Bend arm to 90° - Fix elbow in towards side of body and draw hand backwards HOW TO CONTRACT: Photo A - Press hand forward towards front of body

A

Major muscles stretched Teres major Subscapularis

HOW TO RESTRETCH: Photo B - Take hand backwards and keep elbow stationary

B

Partner External Rotators HOW TO STRETCH: Photo A - Place hand behind back - Bend elbow to 90° - Pull scapula towards spine - Partner to stabilise shoulder and draw hand away from body HOW TO CONTRACT: Photo A - Press hand back towards body

A

HOW TO RESTRETCH: Photo B - Stabilise shoulder - Keep scapula pulled back towards spine - Draw hand further away from spine

B

Major muscles stretched Infraspinatus Posterior deltoid Teres minor

Stick Internal Rotators HOW TO STRETCH: Photo A - Place arm in front of body with elbow at shoulder height - Bend elbow to 90° - Place stick on outside of forearm - Pull on lower part of stick towards centre of body, as in Photo C

C

A

HOW TO CONTRACT: Photo B - Press hand being stretched back towards start position

B

HOW TO RESTRETCH: Photo C - Pull on stick with lower hand, pulling in upward direction

Major muscles stretched Teres major Subscapularis

Internal Shoulder Rotators • Standard: Any • Spring Tension: Medium to Heavy • Muscle Emphasis: Teres major, subscapularis, anterior deltoid, clavicular portion of pectoralis major

A

A. How to stretch Sit on carriage in front of box.

Bend elbows to 90 degrees.

Keep upper arms close to body.

Allow carriage to slide in to find stretch in shoulders.

Use feet to control carriage movement.

B

A. How to contract Press hands into straps in clapping motion.

B. How to restretch Slide carriage further in.

Control movement with legs.

C

C. Variations Carefully turn head and body away from tighter side.

No Box?

Reach around and hold your elbow with one hand and keep it from moving. Allow the carriage to slide in as above.

The subscapularis and teres major are the two muscles stretched the most. The sensations may not be precise, but will stem from anywhere round the shoulder joint.

If you are tight, the pectoralis major – in particular its costal fibers – may stretch, as well as the anterior deltoid.

External Shoulder Rotators • Standard: Any • Spring Tension: Medium to Heavy • Muscle Emphasis: Infraspinatus, teres minor, posterior deltoid

A

A & B. How to stretch Sit on carriage with straps/ropes crossed over. Bend elbows to 90 degrees with straps just above elbows.

Hands on lower lumbar spine.

Allow carriage to slide in to find stretch in shoulders.

B

B. How to contract Press hands into lower back.

C

C. How to restretch Slide carriage further in.

Control movement with legs.

Variations Turn body and head carefully toward tighter side.

Hold the shoulder blades in place; i.e. Don’t permit them to slide away from each other or “protract”. This is done by contracting the trapezius and rhomboid muscles.

If you do this effectively, the infraspinatus, teres minor and posterior deltoid will stretch.

Deltoid • Standard: Any • Spring Tension: Heavy • Muscle Emphasis: Deltoid, rhomboids, middle trapezius

A

A. How to stretch Stand or sit as pictured.

Lean away from strap, ensuring carriage does not move.

Pull arm onto chest with free arm.

A. How to contract Attempt to swing arm holding strap away from chest as if to hit a backhand.

B

B. How to restretch Lift chest and lean further away from strap. Rotate/turn chest away from strap.

C

C. Variation Try seated position.

Lean away from strap.

Keep arm in contact with chest.

Press free hand into shoulder rest to increase leaning-away force.

Contractions as above.

Supraspinatus • Standard: Any • Spring Tension: Heavy • Muscle Emphasis: Supraspinatus, deltoid

A

A & B. How to stretch Stand or sit as pictured.

Lean away from strap ensuring carriage does not move.

B

B. How to contract Attempt to pull elbow away from body.

C

B & C. How to restretch Press free hand into shoulder rest to increase leaning-away force.

Conclusion The stretches that require no equipment can be found in my book “StretchFit: Safe Effective Stretches for Every Body,” on Amazon books.

The final stretches on the Pilates reformer is from “Stretching on the Pilates Reformer: Essential Cues and Images” on Amazon books.