Anatomical Kinesiology (Chapter 5)

How does humeral movement relate to scapular movement?

Flexion/abduction → scapular elevation + upward rotation + abduction
Adduction/extension → scapular depression + downward rotation + adduction
Internal rotation/horizontal adduction → scapular abduction
External rotation/horizontal abduction → scapular adduction

What happens to the scapula during the lifting/pushing phase of a push-up?

Scapular protraction (abduction) — the scapula moves laterally away from the spine.

What muscle weakness can cause scapular winging?

Most commonly serratus anterior weakness/paralysis → medial winging, often due to long thoracic nerve injury.

Less commonly: trapezius and/or rhomboid weakness → lateral winging.

Why is the shoulder joint prone to instability?

Its wide range of motion requires significant laxity, which reduces stability.

• ↑ Mobility → ↓ Stability

• Common problems: rotator cuff impingement, subluxations, and dislocations.

How do you determine if a humerus is the left or right humerus?

Step 1 — Anterior vs. posterior
Anterior → look for the intertubercular (bicipital) groove, where the long head of the biceps tendon runs.
Posterior → bicipital groove is not visible.

Step 2 — Medial vs. lateral
Humeral head = medial (faces toward the body/glenoid).
Greater tubercle = lateral.

Step 3 — Left vs. right
Orient the bone with the humeral head facing medially and the bicipital groove anteriorly.
Then determine which side of the body it fits.

Key check: Head = medial; bicipital groove = anterior.

What type of joint is the glenohumeral joint?

Multiaxial ball-and-socket (enarthrodial) joint.

What is the function of the glenoid labrum?

Slightly enhances stability of the glenohumeral joint.

What is a SLAP tear?

Superior Labrum Anterior to Posterior tear = the superior glenoid labrum is torn from anterior → posterior.

What is the role of the glenohumeral ligaments?

Provide shoulder stability, especially anteriorly and inferiorly. The inferior glenohumeral ligament is particularly important for stability.

Most shoulder dislocations/subluxations occur anteriorly or anteroinferiorly.

What is the difference between a shoulder dislocation and subluxation?

Dislocation = complete separation of the humeral head from the glenoid.

Subluxation = partial/incomplete separation; some joint contact remains.

Why are the glenohumeral joint ligaments relatively lax?

They remain lax through most of the ROM and become taut near extreme ranges of motion, allowing high shoulder mobility at the cost of stability.

• Think: “soggy diaper” → loose/slack normally, but gets pulled tight at the extremes of motion.

Why is it difficult to determine the exact ROM of the glenohumeral joint?

Because glenohumeral movement is accompanied by shoulder girdle/scapular movement, making it difficult to isolate the exact ROM of the glenohumeral joint alone.

• Shoulder joint + shoulder girdle movement → greater total ROM.

• Pure glenohumeral movement alone → much lower ROM.

The accompanying shoulder girdle/scapular movement makes the shoulder’s overall ROM much greater.

What is the pure glenohumeral ROM for abduction and adduction?

Abduction: 90–95°
Adduction: 0° in anatomical position; up to 75° anterior to the trunk.

What is the pure glenohumeral ROM for flexion and extension?

Flexion: 90–100°
Extension: 40–60°

What is the pure glenohumeral ROM for internal and external rotation?

Internal rotation: 70–90°
External rotation: 70–90°

What is the pure glenohumeral ROM for horizontal abduction and adduction?

Horizontal abduction: 45°
Horizontal adduction: 135°

Why is the glenohumeral joint frequently injured, and what instability patterns are common?

• Shallow glenoid fossa

• Lax ligamentous structures

• Lack of muscle strength/endurance

• Anterior or anteroinferior subluxations/dislocations = common

• Posterior dislocations = rare

• Posterior instability = somewhat common

What are the rotator cuff muscles, and what is their main role at the glenohumeral joint?

• SITS = Supraspinatus, Infraspinatus, Teres minor, Subscapularis

• Attach around the front, top, and back of the humeral head

• Allow humeral rotation

• Stabilize/maintain the humeral head within the glenoid fossa while larger muscles move the humerus

• Rotator cuff is frequently injured

What is GIRD, and why is it important?

• GIRD = Glenohumeral Internal Rotation Deficit

• Difference in internal rotation ROM between throwing vs. nonthrowing shoulder

20% GIRD in overhead athletes → higher injury risk

• Stretching to regain internal rotation may:

  • Improve performance

  • Reduce likelihood of injury

Which shoulder joint movements pair with which shoulder girdle movements?

Abduction → Upward rotation
Adduction → Downward rotation

Flexion → Elevation + upward rotation
Extension → Depression + downward rotation

Internal rotation → Abduction (protraction)
External rotation → Adduction (retraction)

Horizontal abduction → Adduction (retraction)
Horizontal adduction → Abduction (protraction)

Scapulohumeral rhythm = coordinated movement of the glenohumeral joint + scapula to produce total shoulder ROM.

Scapulohumeral rhythm = coordinated movement of the glenohumeral joint + scapula to produce total shoulder ROM.

Key ratio = 2:1

• 2° glenohumeral motion

• 1° scapular motion

Example: 170–180° total abduction ≈

• 95° glenohumeral abduction

• 60° scapular upward rotation

• 25° scapular elevation

Key idea: GH + scapular movements are synergistic, not necessarily sequential. The 2:1 ratio may vary between individuals.

movments…

What is the difference between glenohumeral abduction and adduction?

Abduction → humerus moves upward/laterally out to the side, away from the body.

Adduction → humerus moves downward/medially toward the body from an abducted position.

What is the difference between glenohumeral flexion and extension?

Flexion → humerus moves straight anteriorly (forward).

Extension → humerus moves straight posteriorly (backward).

What is the difference between glenohumeral horizontal adduction and horizontal abduction?

Horizontal adduction → humerus moves across/toward the chest in the horizontal (transverse) plane.

Horizontal abduction → humerus moves away from the chest in the horizontal (transverse) plane.

What is the difference between glenohumeral external and internal rotation, and what scapular movements accompany them?

External rotation → humerus rotates laterally, away from midline
→ Scapular adduction (retraction)

Internal rotation → humerus rotates medially, toward midline
→ Scapular abduction (protraction)

What is the difference between diagonal abduction and diagonal adduction of the shoulder?

Diagonal abduction → humerus moves diagonally away from the midline.

Diagonal adduction → humerus moves diagonally toward the midline.

Intrinsic vs. extrinsic glenohumeral muscles

• Intrinsic glenohumeral muscles:

  • Originate on the scapula or clavicle

  • Deltoid

  • Coracobrachialis

  • Teres major

  • Rotator cuff group:

    • Subscapularis

    • Supraspinatus

    • Infraspinatus

    • Teres minor

• Extrinsic glenohumeral muscles:

  • Latissimus dorsi

  • Pectoralis major

Which glenohumeral muscles are anterior vs. superior?

• Anterior:

  • Pectoralis major

  • Coracobrachialis

  • Subscapularis

• Superior:

  • Deltoid

  • Supraspinatus

Which glenohumeral muscles are superior vs. posterior?

• Superior:

  • Deltoid

  • Supraspinatus

• Posterior:

  • Latissimus dorsi

  • Teres major

  • Infraspinatus

  • Teres minor

What nerves innervate the shoulder joint muscles shown on this slide?

• All shoulder joint muscles are innervated by branches of the brachial plexus.

• Lateral pectoral nerve:

  • Roots: C5, C6, C7

  • Innervates pectoralis major, clavicular head

• Medial pectoral nerve:

  • Roots: C8, T1

  • Innervates pectoralis major, sternal head

• Thoracodorsal nerve:

  • Roots: C6, C7, C8

  • Innervates latissimus dorsi

What nerves innervate the deltoid, teres minor, and subscapularis?

• Axillary nerve:

  • Roots: C5, C6

  • Innervates:

    • Deltoid

    • Teres minor

  • Sensory:

    • Lateral patch of skin over the deltoid region of the arm

• Upper subscapular nerve:

  • Roots: C5, C6

  • Innervates:

    • Subscapularis

What nerves innervate the subscapularis, teres major, supraspinatus, and infraspinatus?

• Lower subscapular nerve:

  • Roots: C5, C6

  • Innervates:

    • Subscapularis

    • Teres major

• Suprascapular nerve:

  • Roots: C5, C6

  • Innervates:

    • Supraspinatus

    • Infraspinatus

What are the roots, motor function, and sensory function of the musculocutaneous nerve?

Musculocutaneous nerve:

• Roots: C5, C6, C7

• Motor:

  • Coracobrachialis

• Sensory:

  • Radial aspect of the forearm

What are the actions of the deltoid muscle fibers?

• Anterior fibers:

  • Abduction

  • Flexion

  • Horizontal adduction

  • Internal rotation

• Middle fibers:

  • Abduction

• Posterior fibers:

  • Abduction

  • Extension

  • Horizontal abduction

  • External rotation

What are the actions of the upper and lower fibers of the pectoralis major?

• Upper fibers (clavicular head):

  • Internal rotation

  • Horizontal adduction

  • Flexion

  • Assists with abduction once arm is abducted 90°

  • Adduction when arm is below 90° of abduction

• Lower fibers (sternal head):

  • Internal rotation

  • Horizontal adduction

  • Extension from a flexed position

  • Adduction

Memory tip:

• Upper fibers = “UP and ACROSS”

• Lower fibers = “DOWN, BACK, and ACROSS”

• Both share: internal rotation + horizontal adduction

What are the actions of the latissimus dorsi?

• Adduction

• Extension

• Internal rotation

• Horizontal abduction

Memory tip:

• Adduction = arm moves toward the body

• Extension = arm moves backward

• Internal rotation = humerus rotates inward

• Horizontal abduction = arm moves backward in the horizontal plane