Muscle Analysis: The Shoulder Girdle

3 anterior muscles

  • SA - Serratus anterior
  • PECmnr - Pectoralis minor
  • SUBC - Subclavius (not a PM)

3 posterior muscles

  • LS - Levator scapula
  • RHOM - Rhomboids
  • TRAP - Trapezius

Abduction/Protraction

Transverse plane, Longitudinal axis

  • SA - Serratus anterior
  • PECmnr - Pectoralis minor
  • (SUBC - Subclavius (not a PM))

Adduction/Retraction

  • TRAP - Trapezius (mid + lower)
  • RHOM - Rhomboids
  • (LS - Levator scapula)

Elevation

Frontal plane, Sagittal axis

  • TRAP - Trapezius (upper)
  • LS - Levator scapula
  • RHOM - Rhomboids

Depression

  • PECmnr - Pectoralis minor
  • (SUBC - Subclavius (not a PM))
  • TRAP - Trapezius (lower)

Upward rotation

Frontal plane, Sag. axis

  • TRAP - Trapezius (mid and lower)
  • SA - Serratus anterior

Downward rotation

  • PECmnr - Pectoralis minor
  • RHOM - Rhomboids
  • (LS - Levator scapula)

PADDEL: Posterior muscles ADDuct and ELevate

Arthrodial Joints

Articulating Bones

Sternoclavicular (SC)

Manubrium (sternum)

Clavicle (Medial/sternal end)

Acromioclavicular

Acromion (of scapula)

Clavicle (Lateral end)

Shoulder Girdle movement definitions:

Arthrodial/gliding joint: 2 flat bony surfaces that butt against each other.

Adduction/Retraction: movement of the scapula medially towards the spinal column, as in pinching the shoulder blades together (Transverse plane, longitudinal axis)

Abduction/Protraction: movement of the scapula laterally away from the midline, as in reaching for an object in front of the body (Trans. plane, long. axis)

Elevation: Upward/superior movement as in shrugging the shoulders (Frontal plane, sag. axis)

Depression: Downward/inferior movement as in returning to a normal position from a shoulder shrug

Upward rotation: turning the glenoid fossa up and moving the inferior angle upwards and laterally away from the spinal column (frontal plane, sag. axis)

Downward rotation: returning the inferior angle medially and inferiorly toward the spinal column, and the glenoid fossa to its normal position (frontal plane, sag. axis)

Serratus Anterior

Origin

Axial Skeleton

1st through 9th ribs

On surface, at side of chest

Insertion

Shoulder Girdle – Scapula

Anterior, medial border

SG Action

Abduct – Scapula

Upward Rotation – Scapula

Pectoralis minor

Origin

Axial Skeleton

3rd through 5th ribs

Anterior surface

Insertion

Shoulder Girdle – Scapula

Coracoid process

SG Action

Abduct – Scapula

Downward Rotation – Scapula

Depression – Scapula

Subclavius

Origin

Axial Skeleton

1st rib 

Superior aspect at junction with costal cartilage

Insertion

Shoulder Girdle – Clavicle

inferior groove in mid portion

SG Action

Depression – Clavicle

Abduction – Clavicle

Levator Scapulae

Origin

Axial Skeleton

C1-C4

Transverse processes

Insertion

Shoulder Girdle – Scapula

medial border above spine

SG Action

Elevation – Scapula

(Downward rotation)

(Adduction)

Rhomboids

Origin

Axial Skeleton

C7 – T5

Spinous processes

Insertion

Shoulder Girdle – Scapula

medial border below spine

SG Action

Adduct – Scapula

Downward rotation – Scapula

Elevation – Scapula

Trapezius

Origin

Upper portion:

Axial Skeleton – Skull

Occipital protuberance and C6, and lateral to acromion

 

Middle portion:

Axial Skeleton – C7 – T3

Spinous processes

 

Lower portion:

Axial Skeleton – T4 – T12

Spinous processes

Insertion

Upper portion:

Shoulder girdle – Clavicle

posterior, lateral 1/3rd of Clavicle

 

Middle portion:

Shoulder girdle – Scapula

Medial border acromion process and superior border of spine of scapula

 

Lower portion:

Scapula

base of spine of scapula

SG Action

Upper portion:

Elevate Scapula

Extend and rotate head at neck

 

Middle:

Elevate – scap

Upward Rotation – scap

Adduction  – scap

 

Lower:

Depress scap

Adduct scap

Upward rotation of scap

Line of Pull

Pectoralis major (clavicular head) is primarily a flexor, but when in anatomical position, the clavicular portion of PECmjr acts as a strong adductor and internal rotator of the humerus.

Acting independently, the clavicular portion of the muscle flexes the humerus up to 90 degrees in a horizontal plane. The sternocostal portion of the muscle can produce the antagonistic movement and extend the humerus back to the anatomical position. 

Acting together with the of latissimus dorsi muscle, the pectoralis major muscle pulls the trunk forwards or upwards when its humeral attachment is fixed. This action is important in activities such as climbing. When acting from the humeral attachment, the pectoralis major muscle also facilitates the act of inspiration. This is particularly important during forced breathing in physical distress.

Consider the line of pull and direction of muscle fibers

Things to consider

  1. Exact locations of bony landmarks to which muscles attach proximally and distally
  2. The muscle’s relationship/line of pull relative to the joint’s planes of motion and axes of rotation
  3. The planes of motion and corresponding axes through which a joint is capable of moving
  4. As a joint moves through a particular ROM, the ability of the line of pull of a particular muscle to change and even result in the muscle having a different or opposite action than the original position.
  5. The potential effect of other muscles’ relative contraction or relaxation of a particular muscle’s ability to cause motion
  6. The effect of a muscle’s relative length on its ability to generate force (e.g. active/passive insufficiency and length-tension relationship)
  7. The effect of the position of the other joints on the ability of a bi-articular or multi-articular muscle to generate force or allow lengthening.

*Information from my college course on Structural Kinesiology with Dr. Jane Roy at UAB, 2010.

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