Muscle Analysis: The Shoulder Joint

Instead of tossing out my Kinesiology notes from college, I’m documenting the information here.

3 anterior muscles

  • Pectoralis major (E)
  • Coracobrachialis (I)
  • Subscapularis* (I)

2 superior muscles

  • Deltoid (I)
  • Supraspinatus* (I)

4 posterior muscles

  • Latissimus dorsi (E)
  • Teres major (I)
  • Infraspinatus* (I)
  • Teres minor* (I)

* 4 muscles = rotator cuff group. Main function: hold socket, stabilize, especially during eccentric joint deceleration

I – intrinsic (7): originate on the Shoulder girdle and inserts on the shoulder girdle

E – extrinsic (2): originate on the outside of the shoulder girdle (ex. sternum, ribs, vertebrae)

Shoulder Extension - 7 muscles

Sagittal plane, Frontal axis

  • Deltoid (P)
  • Pectoralis major (L)
  • Subscapularis
  • Latissimus dorsi
  • Teres major
  • Infraspinatus
  • Teres minor

Shoulder Flexion - 3 muscles

  • Deltoid (A)
  • Pectoralis major (U) (0-60 degrees)
  • Coracobrachialis

Horizontal Adduction - 3 muscles

Transverse plane, Sag. axis

  • Deltoid (A)
  • Pectoralis major (U & L) (0-60 degrees)
  • Coracobrachialis

Horizontal Abduction - 4 muscles

  • Deltoid (A)
  • Latissimus dorsi
  • Infraspinatus
  • Teres minor

Adduction - 5 muscles

Frontal plane, Sag. axis

  • Pectoralis major (U & L) (0-60 degrees)
  • Coracobrachialis
  • Subscapularis
  • Latissimus dorsi
  • Teres major

Abduction - 3 muscles

  • Deltoid (A, M, P)
  • (Supraspinatus)
  • Pectoralis major (>90 degrees, U)

External Rotation - 3 muscles

Transverse plane, Longitudinal axis

  • Teres minor
  • Infraspinatus
  • Deltoid (P)

Internal Rotation - 5 muscles

  • Deltoid (A)
  • Pectoralis major (>90 degrees, U)
  • Subscapularis
  • Latissimus dorsi
  • Teres major

Shoulder (glenohumeral) joint

Classification:

Ball and socket. Enarthrodial

Articulating bones:

(Glenoid fossa) Scapula and proximal head of humerus

Movements:

AB & AD, Flex & Ext, Internal rotation, external rotation

Increased mobility and decreased stability due to:

  1. Very shallow glenoid fossa
  2. Ligaments are lax
  3. Lack of strength and endurance in stabilizing muscles (rot. cuff)

The rotator cuff is for stability and easily injured.

What bones serve as attachments for most muscles of the Shoulder joint?

Humerus

Clavicle

(Sternum)

(Vertebrae)

Scapula

 

Pairing of shoulder girdle and shoulder joint movements: The SJ and SG work together in carrying out UE movements. SG muscles provide essential ______ of the scapula, so the muscles of the SJ will have a stable base from which to move (eg tricep dips). The SG can also go through a more extreme ROM so that the ________ is in a more appropriate position from which the humerus can move (eg lateral side raise)

Shoulder Joint

Shoulder Girdle

Abduction

upward rotation/elevation

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)

Shoulder Joint movement definitions:

Enarthrodial/ball and socket/multiaxial: permits movement in 3 planes

Abduction: upward lateral movement of the humerus, in the frontal plane (sagittal axis) out to the side, away from the body

Adduction: downward movement of the humerus in the frontal plane (sagittal axis) returns the body from abduction

Flexion: movement of the humerus straight anteriorly from any point in the sagittal plane (frontal axis)

Extension: movement of the humerus straight posterior from any point in the sag. plane (frontal axis)

Internal rotation: movement of the humerus in the transverse plane around its longitudinal axis toward the midline

External rotation: movement of the humerus laterally in the transverse plane around its longitudinal axis away from the midline

Horizontal abduction: movement of the humerus in a horizontal/transverse plane away from the chest (longitudinal axis)

Horizontal adduction: movement of the humerus in a horizontal/transverse plane towards the chest

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