OT 450 Biomechanics of Human Occupation: Shoulder 2

Let's analyze this interesting posture:

Description: Description: picture of individual from back with arms behind back and hands together in "praying" position

Motion / Position Observed

Approximate Joint Position

Effect of Gravity

Active Muscle Group / Contraction Type

Scapulo-thoracic joint: retracted, "tipped" forward so that the inferior angles are pushing out away from the thorax

100% retracted

none really - the main force the position is begin held against is stretch of the protractors, trying to recoil and pull the scapulae forward away from this extreme retraction

retractors (rhomboids and middle trap) isometric to hold position

Shoulder joint: internally rotated/adducted/hyperextended

each humerus 90+ deg. (100%) internally rotated at GH joint; 0% abducted; <50% hyperextended

again - the main opposing force is stretch of the opposite tissue: stretched external rotators

GH adductors and internal rotators isometric to hold position

Elbow joint: flexion

slightly >50% flexed (a little more than 90 deg. flexed)

elbow extension

maybe some activity (isometric) in elbow flexors; but mostly held in position due to strong should adduction forcing hands together in midline

Proximal/distal radioulnar joints: pronated

nearly 100% (close to 90 deg.)

mostly irrelevant - everything under tension of tissues

possibly some isometric forearm pronators

Wrist joints: extended

nearly 100% (almost 90 deg.)

flexion (but another force against which this wrist extension is begin held is the stretch and potential recoil of the wrist and finger flexors being stretched - tending to pull the wrists into flexion away from this extreme position of extension

probably none - everything is held in place by the tension created at the shoulder: "cocking" the shoulders into extreme internal rotation and locking them in place by placing the forearms behind the back, then adducting the shoulders is what keeps the wrists extended

A closer look at some of the segments/muscles: Three Parts of the Trapezius -

Note where each attaches to the scapula: Upper goes laterally onto the spine of the scapula; middle to the middle of the spine of the scapula; lower fibers travel upwardly to attach to the most medial aspect of the scapular spine.

Description: Description: illustration of full trapezius on left and  rhomboids and levator scapulae on right

Scapular Winging – loss of serratus anterior

Pushing against the wall (“wall test”) requires protraction – see it on the left, not on the right

Description: Description: photo showing person pushing against wall with right scapulawinging away from trunk

Lack of Upward Rotators of Scapula:

Here the problem is inability to Upwardly Rotate Scapula after the command, “Raise your hand above your head.” The scapula downwardly rotates because there are no upward rotators to counterbalance the weight of the arm pulling the scapula down. The GH joint moves fully into 90 degrees abduction – but it doesn't’t look so unless you look at the angle between the scapula and the humerus itself (red lines try to illustrate this with one red line going along the vertebral border of scapula - which should be angled up, not down - and other line going through humeral shaft).

Description: Description: photo of someone attempting upward reaching but because of lack of upward sacapular rotators shows arms at about 45 degree angle away from  trunk with scapulae downwardly rotated

Functional Considerations: Shoulder Abduction

·         Stabilization of the scapula (click on this link)

·         Early activation of the supraspinatus

·         Stabilization of humeral head (click on the link) via inferior rotator cuff muscles

·         Scapulohumeral rhythm:

·         After about 30 deg. GH abduction, GH abduction and scapular upward rotation accompany each other

Here is a comparison of normal reach on one side with restricted reach and compensation via scapular elevation:



Or watch on You Tube site: http://www.youtube.com/watch?v=Zt1QM1bzi-8

Once again, it is time to study some representative muscles in the Online Atlas.

Study AJRAO for:

  • latissimus dorsi,

  • pectoralis major,

  • supraspinatus & infraspinatus,

  • deltoid

Latissimus Dorsi & Pectoralis Major

Or go to YouTube site to view: http://www.youtube.com/watch?v=4lbAA4_S-XM

Bone Background:

Specific bony landmarks are presented at the end of this page for reference regarding muscle attachments. Before beginning this construction, look at the Get Body Smart site and review appropriate bony landmarks.

Orientation - left posterior trunk with scapula:

Description: Description: W:\Functional_Mechanical_Antomy\OT450_PowerPoints\Shoulder\jpg\orientation_shots\Left_scap-trunk_postView.jpg

Latissimus Dorsi

You Tube Link: http://www.youtube.com/watch?v=BNXF_SaIayE

Description: Description: latissimus dorsi with insert showing latissimus insertion next to and in front of teres major insertion

Origin: Spines of lower thoracic vertebrae, sacrum by way of lumbodorsal fascia, crest of ilium;

Insertion:Floor of bicipital groove;

Action: Internal rotation, adduction and extension of the UE at the shoulder; also assists in raising the trunk for transfers through closed-chain scapular depression; Function: shoulder extension and trunk elevation in transfers. Antagonist motion allowed: External rotation, abduction, flexion.

Nerve: Thoracodorsal nerve

Construction Notes:

Attach origin first; as you go to attach the insertion, pass in front of the teres major.


Description: Description: head, neck, trunk anterior view

Pectoralis Major

Description: Description: insertion of sternal portion of pectoralis major

Description: Description: pectoralis major

Origin: Medial half of clavicle, sternum and costal cartilages down to 7th rib;

Insertion:Lateral lip of bicipital groove;

Action: Internal rotation, adduction of the UE at the shoulder; clavicular portion flexes UE from 0 degrees; sternal portion extends from flexed position and hyperextends; Function: Assists in shoulder flexion and internal rotation as used in reaching above head into a kitchen cabinet. Antagonist motion allowed: External rotation, abduction, flexion (stretch of sternal portion mainly).

Nerve: Medial and lateral pectoral l nerves

Construction Notes:

(A) Attach the sterno-costal portion first at its origin (sternum). As you move to attach the insertion to the proximal humerus, do two things:(1) twist the fabric 180 degrees so the lower edge is now highest; (2) attach the twisted insertion-end of the muscle to the highest part of the lateral lip of the bicipital groove. (B) Next attach the clavicular portion - insertion is not twisted but is attached inferior to (below) the insertion of the sternal portion of the muscle.

Supraspinatus, Infraspinatus, Deltoid


Bone Background:

Specific bony landmarks are presented at the end of this page for reference regarding muscle attachments. Before beginning this construction, look at the Get Body Smart site and review appropriate bony landmarks.

Construction Notes:

You will be working on the right scapula for these muscles. There are a few things to do that might make it easier later for muscle attachments: (1) remove the two screws attaching the bracket to the humeral head to gain access to the screw holing the bracket itself into the glenoid. (2) Loosen the screw a bit to allow the bracket (and therefore the humeral head once you reattach it) to slightly sublux (partially dislocate inferiorly). This is to give you more room to work on muscle attachments. (3) Skip to Week 9 to attach the origins of the long head of the biceps brachii and the long head of the triceps brachii; then return to this lab once those two origins are attached.


Description: Description: W:\Functional_Mechanical_Antomy\OT450_PowerPoints\Shoulder\jpg\orientation_shots\right_UE_trunk_postView.jpg

Supraspinatus (posterior view right scapula)

Description: Description: supraspinatus

Origin: Supraspinatus fossa;

Insertion: Top of greater tubercle of humerus (greater tubercle is continuous with the lateral lip of bicipital groove below);

Action: Abduction of the humerus at the shoulder - works together with deltoid in this action much of the time; Function: raising the hand out or above the head to reach above the head in cabinets or to ask a question in class! Antagonist motion allowed: Shoulder adduction.

Nerve: Suprascapular nerve (spinal nerve C5)

Construction Notes:

You may have to either stretch the glenohumeral joint by putting distal traction on the humerus or you will have to loosen the screw into the glenoid (as described at the beginning of this lab) holding the humerus to the scapula - do this in order to have a little more room to pass the supraspinatus under the acromion to attach the insertion.


Description: Description: infraspinatus

Origin: Infraspinatus fossa of the scapula;

Insertion:greater tubercle of humerus, just below the supraspinatus;

Action: External rotation of humerus (notice the dark-blue color compared to the subscapularis, which is light-blue as an internal rotator; also notice the supraspinatus is not a rotator at all - but a pure abductor); Function: Positioning the hand behind the back to put the second sleeve of the shirt on when dressing; also important biomechanical function along with the subscapularis of depressing the head of the humerus during heavy activation of the deltoid early in shoulder abduction. Antagonist motion allowed: Internal rotation.

Nerve: Suprascapular nerve (spinal nerve C5, 6)

Construction Notes:

Be sure to cut the Infraspinatus in a way that the lateral border of the scapula is available for attachment of the teres minor.


Description: Description: W:\Functional_Mechanical_Antomy\OT450_PowerPoints\Shoulder\jpg\orientation_shots\shoulder_box_ant.jpg

Deltoid (Left shoulder, anterior view: Anterior & Middle shown in left frame; Left shoulder, posterior view: Posterior & Middle shown in right frame)

Description: Description: deltoid anterior middle posterior

Origin: Lateral portion of scapular spine, acromion, lateral portion of clavicle;

Insertion:deltoid tubercle on lateral proximal 1/3 of humerus;

Action: Middle Deltoid abducts humerus (green); Anterior Deltoid flexes and helps to internally rotate humerus (yellow & light-blue); Posterior Deltoid extends and helps to externally rotate humerus (orange & dark-blue); Function: Positioning the hand above the head to reach into cabinets or to put the hands and arms through a T-shirt when donning a T-shirt. Antagonist motions allowed: Humeral adduction - but because gravity always holds the humerus in full adduction, this muscle rarely develops a contracture. However, in the case of wearing an airplane splint - holds the humerus in 90 degrees abduction to protect the supraspinatus after injury/surgery - a contracture develops and adduction typically is limited.

Nerve: Axillary nerve (spinal nerve C5, 6)

Construction Notes:

Add all three portions of deltoid to the left shoulder: place middle first, then posterior, then anterior.

Below are charts of important bones and tubercles, some serving as attachment locations for muscles:


Description: Description: scapula and its prominences and angles

A = spine of scapula with root of spine medial and ending in acromion process laterally (arrow)

B = lateral portion of clavicle serving as distal attachment of trapezius upper fibers and proximal attachment of deltoid anterior fibers

C = Lateral border serving as proximal attachment of teres minor and teres major (mostly the lower lateral border and inferior angle - E)

D = vertebral border serving as distal attachments of both rhomboids and serratus anterior (from deep side)

E = Inferior angle

F = superior angle - attachment of levator scapulae

G = glenoid - socket for head of humerus in glenohumeral joint; in living tissue this socket is deepened by the presence of the glenoid labrum


Description: Description: W:\Functional_Mechanical_Antomy\OT450_PowerPoints\Shoulder\down-pull-on-humerus-icon.jpgDownward Pull on Humerus

Description: Description: W:\Functional_Mechanical_Antomy\OT450_PowerPoints\Shoulder\closed_shoulder_icon.jpgClosed-Chain Shoulder Motion


Continuing with biomechanics . . . Which muscles to strengthen for independence in transfer? (click on the picture)

Description: Description: figure showing interactive exercise link

Now on to analyze what's happening in the above interactive exercise - when someone anchors the hand on the mat top and tries to (contracts the muscles to) depress the scapula, and the trunk elevates instead:

Motion / Position Observed

Approximate Joint Position

Effect of Gravity

Active Muscle Group / Contraction Type

What we see in the interactive exercise:

Trunk motion at scapulo-thoracic joint: During the lift of the transfer, trunk elevates with respect to scapula instead of scapula depressing

full elevation of trunk = pelvis raised off of mat

to pull trunk down to mat

scapular depressors (latissimus dorsi) are concentrically contracting: as they "attempt" to pull their attachment on the scapula downward toward their attachment to the lower trunk, the hand anchored to the mat surface cannot push down further into the mat, and its linkage to the scapula through the extended elbow and adducted glenohumeral joint prevents the scapula from depressing; as latissimus dorsi continues to shorten, it moves whatever end of the muscle can move - so the lower trunk is raised up toward the scapula, and this raises the seat off of the mat for either a transfer or pressure release.

Also happening elsewhere in the upper extremity: Wrist joint: Extended entire time bearing weight of trunk

90 degrees (100%)

wrist extension because the weight of the upper trunk and arm are pushing the upper extremity downwardly and with the palm on the mat, the wrist is forced into extension

none needed

Elbow joint: Extended entire time bearing weight of trunk

0 deg. (0%) flexed (fully extended = 100% extended)

elbow flexion - if there was no muscle activity across the elbow in this position, the weight of the upper trunk (gravity) would push the elbow into flexion since the hand is anchored on the mat

elbow extensors isometric contraction

Shoulder joint (Glenohumeral joint): extended/adducted getting ready for transfer

0 deg. (0%) flexed/abducted (full or 100% extension/ adduction)

Considering the upright position sitting on mat before the lift, if trunk is stable, gravity simply keeps shoulder in anatomical position – sh. extended and adducted - humerus in line with trunk; _____________________________

While trunk pulled up and suspended, trunk may sway forward/backward and pull of gravity may cause closed chain shoulder extension and flexion alternately

Sitting upright, ready for transfer, no shoulder mm. contractions needed

If trunk sways as a pendulum while lifting off mat will see stabilization primarily  via the shoulder using shoulder flexors and extensors alternately or cocontracting to prevent motion of trunk


You also can point your browser to You Tube to watch the movie:




So what's happening here? Here is an analysis of Skip using his shoulder or scapular depressors to raise the trunk for a pressure release. This is same as above, but watching as Skip does it in real context.

Motion / Position Observed - as performs pressure release

Approximate Joint Position

Effect of Gravity

Active Muscle Group / Contraction Type

Elbow joint: flexed; moves into extension as he raises out of his seat

90 deg. (50%) flexed to begin; moves to less flexion (about 45 deg. flexion) as trunk elevates

elbow flexion - as the elbow extends during trunk elevation, gravity's effect on the raised trunk is to pull it down - this would flex the elbow

elbow extensors concentric contraction to move into elevation; isometric to hold up in the air; eccentric to control lowering by force of gravity (weight of the trunk)**

Shoulder joint: Begins extended/adducted

0 deg. (0%) flexed/abducted (full or 100% extension/ adduction)

shoulder extension/adduction (if the shoulder were flexed or abducted from this position, gravity would extend/adduct it and hold it in extension/adduction in the position seen)

Held by position he is in - little muscle contraction to maintain this starting position

Shoulder joint: Moves toward flexion as trunk elevates for pressure release

moves about 15 or 20 degrees to get from hyperextension to neutral (aligned with trunk)

Gravity effect on trunk - pulling it down - results in gravity pushing the shoulder back toward hyperextension

What do you think? Also - don't forget contraction needed to slowly lower trunk back down (see elbow joint above)

Trunk motion at scapulo-thoracic joint: trunk elevates with respect to scapula instead of scapula depressing - notice earlobe is aligned with top of shoulder before beginning and earlobe ends up 3 or 4 inches above shoulder when trunk fully elevated

full elevation of trunk = pelvis raised off of wheelchair seat surface

??????What do you think??????

????What do you think???? (Click here to see completed BMA.)

**This isometric contraction to control lowering of the trunk is crucial. If Skip simply stopped the contraction at the top of trunk elevation, the trunk would accelerate downwardly and his bottom would hit the wheelchair seat surface with enough force to possibly cause a bruise and lead to skin breakdown.


Normal (left) Dislocated (right)

Description: Description: xray normal shoulder jointDescription: Description: xray dislocated shoulder joint

Right-hand xray, upper arrow points to glenoid fossa ("socket") and lower arrow points to humeral head which is dislocated and appears below and in front of glenoid.

"A-C Sprain" or "Shoulder Separation":

Description: Description: xray "shoulder separation" or A-C joint sprain

Shoulder Subluxation as is Common with CVA

Description: Description: xray of subluxed humeral head or "shoulder subluxation"

Description: Description: xray of normal GH joint

Red circle indicates glenoid fossa - the "socket" for the humeral head. Notice on the left the humeral head has "drooped" inferiorly - this is subluxation (incomplete dislocation). In the right figure, the humeral head has been supported and raised up to align with the glenoid. The support device is a sling called the "GivMohr Sling

" (shown below):

Description: Description: photo of person wearing GivMohr sling

Normal Biomechanical Mechanism to Prevent Shoulder Subluxation

Description: Description: link to subluxation interactive exercisehttp://www.myCHHS.colostate.edu/David.Greene/GH_sublux_page.htm

GH dislocation via forceful abduction in case of tight adductors

Description: Description: link to GH dislocation interactive exercise

This can happen in the case that a therapist is forcefully ranging someone with tight adductors - especially pectoralis major. Since after CVA, the rotator cuff muscles closely surrounding the humeral head become lax but the adductors/extensors develop spasticity, it is important to range the shoulder to maintain full flexion and abduction. However, ranging must occur slowly to allow the muscle spindles to adapt and allow the muscle to relax as stretched. If ranged to quickly, the pec major does not "give", and with loose rotator cuff muscles, the insertion of the pec major becomes the stationary point and the GH joint dislocates as the head of the humerus moves instead of being the center of rotation. Be sure to click on the image and attempt the interactive exercise!

Substitution of biceps (long head) for weak abductors

Description: Description: figure showing long head of biceps as GH abductor after external rotation of humerus at GH joint

Just a little tidbit of minutia: In cases where an individual has severe weakness in the middle deltoid and supraspinatus, it is a common learned adaptation (learned through trial and error), when asked to move the arm out to the side to place hand over head (in other words, to abduct the UE at the shoulder), to first "spin" the arm outwardly (laterally rotate) and then feel more strength to abduct. The figure tries to illustrate that in anatomical position, the long head of the biceps is in front of the shoulder - and not in a position to abduct. But after external rotation, the tendon of the long head of the biceps is in a lateral position with respect to the shoulder - just like the middle deltoid - and serves as an abductor.


STOP HERE AND GO to Learning Modules First Shoulder BMA to check out your own ability to perform biomechanical analysis involving the shoulder!