Functional Roles of Upper Limb Muscles

Question 1

What does rhomboid major do to the scapula?

Answer 1

Rhomboid major medially rotates the scpaula

Question 2

When active as an agonist, what do the shoulder flexors do to the humeral head?

Bonus points for further info!

Answer 2

The shoulder flexors, the clavicular head of pec major, coracobrachialis and anterior delt, translate the humeral head anteriorly.

Bonus point: thus, the posterior rotator cuff will be recruited to pull humeral head back

Question 3

Is the internal or external rotation of the shoulder desired during shoulder flexion?

Answer 3

external rotation!

Question 4

What is the significance of the relationship between the RC and scapula?

Answer 4

Axioscapular muscles work harder when RC work harder in order to keep scapula stable

Explanation: (TLDR: When RC on, scapula kept stable by axioscap muscles)

Load the axioscapular muscles by loading the stabilising role → cant hold scapula whilst its rotating → but we can load deltoid, pecs, lats etc , thus requiring RC to work harder, thus the axioscapular muscles have to work harder

Question 5

When are upper and lower traps recruited as stabilisers?

Answer 5

in shoulder flexion + abduction / whenever they are recruited as agonists

Question 6

Name the two non directional stabilisers during shoulder movements

Answer 6

Serratus Anterior and Rhomboids

Explanation: (muscles attaching from humerus to scapula..anytime they contract) Stop lateral translation of scap → move scap against body to provide medial force → anything attached to scap will do this (SA, rhomboids)

Question 7

What are the six patterns of movement across the shoulder?

Answer 7

abduction/adduction

flexion/extension

internal/external rotation

Question 8

What are the agonists during shoulder extension at GHJ and scapula? What actions are they performing?

Answer 8

GHJ: Lat dorsi, teres major, posterior delt, and triceps –> shoulder ext

Scap: rhomboid major/minor and levator scap –> med. rot of scap

Question 9

What are the stabilisers of the humerus and scapula during shoulder extension?

Bonus points: explain!

Answer 9

humerus: Subscap!

Scapula: Rhomboid major/minor, Serratus Anterior, Lower Trapezius

Explanation:

Ant. RC (sub scap) stabilizes GHJ by preventing posterior translation caused by agonists

R major/minor, SA and LT stabilizes scap to provide stable base for scapulohumeral muscles to work off and prevent them from pulling scapula laterally; prevent lateral translation of scapula

Question 10

What does Lat Dorsi do during the pitching throwing motion in each of the three phases?

Answer 10

during all phases, the lats also provide GHJ stability by providing a posterior translation force to balance the pec’s anterior translation And probably a medial and inferior stabilising force

Cocking phase:

internally rotates - cancels out excessive external rotation

Acceleation Phase:
- main force generator and stabiliser at GHJ
- acts as synergist to cancel out excessive abduction from deltoid

Deceleration Phase:
- provide trunk stabliity by create tensions to TLF

Question 11

What is the significance of the decelerators in relation to the joint?

Answer 11

deceleration occurs to prevent instability

therefore it protects the joint

Question 12

What is a ‘non direction specific’ stabiliser? How does it differ from a direction specific stabiliser?

Answer 12

• those which stabilise the scapula whether they are acting as a mover or not (SA and rhomboids).
• “Direction specific” stabilisers only become a stabiliser when they act as movers (Upper traps, lower traps)

Question 13

Provide an example to Compare and contrast direction specific and non directional stabilisers

Answer 13

during full range shoulder abduction, you would need lateral rotation of the scapula, which requires upper and lower traps to act as movers, hence the direction specific stabilisers are working in addition to non-direction specific (SA, rhomboids)

However, during shoulder extension, you do not need lateral rotation of scapula, so UT/LT won’t be active as movers and hence they are not recruited as stabilisers. However, you still need SA and rhomboids to activate (the non-direction specific stabilisers)

Question 14

What does Lat dorsi during cocking phase?

Answer 14

during all phases, the lats also provide GHJ stability by providing a posterior translation force to balance the pec’s anterior translation And probably a medial and inferior stabilising force

Cocking phase:

internally rotates - cancels out excessive external rotation

Question 15

What does Lat Dorsi do during Acceleration Phase?

Answer 15

Acceleation Phase:
- main force generator and stabiliser at GHJ
- acts as synergist to cancel out excessive abduction from deltoid

Question 16

What does Lat Dorsi do during Deceleration Phase?

Answer 16

Deceleration Phase:
- provide trunk stabliity by create tensions to TLF

Question 16

Explain the result of RC dysfunction/weakness.

Answer 16

Using the posterior RC to achieve shoulder extension avoids use of the lats.
The lats cause posterior translation of the humeral head.
If anterior RC is dysfunctional or weak, posterior translation cannot be prevented.
Shoulder extension via lats and posterior delt causes shoulder pain.
To avoid pain posterior RC takes on the role of shoulder extension.

Question 17

Explain what could result in RC dysfunction/weakness.

Answer 17

Use of posterior RC to achieve shoulder extension does not require a stable scapular and does not cause posterior translation of the humeral head.
Unstable scapula during shoulder extension means the axioscapular muscles rhomboid major and minor are not turned on.
If there is no posterior translation subscapularis is not turned on during shoulder extension.
Lack of stimulus does not require subscapularis and axioscapular muscles to increase in strength.
Anterior RC and axioscapular muscle weakness/dysfunction is exacerbated.

Question 18

How does scapular movement serve the GHJ?

Answer 18

▪occurs to “serve” the shoulder joint by:
• repositioning the glenoid fossa thus increasing the available range of movement at shoulder joint
• repositioning the scapulohumeral (RC, deltoid, teres major) muscles to maintain optimal mechanical alignment through shoulder joint range of motion
▪produces movement of the clavicle at the sternoclavicular and acromioclavicular joints
• rotation of the clavicle produced via tension in conoid ligament
movement

Question 19

What are the main reasons for scapula rotation?

Answer 19

1) avoid pain
2) providing sufficient articulate surface for numeral head to move on
3) so the greater tubercle clears the coracoacromial arch

Question 20

What muscles cause lateral translation of the scapula?

Answer 20

The scapulohumeral muscles; namely deltoid, RC, Teres major

Explanation: when the scaoulohumeral muscles contract, the scapula moves away from the spine

Question 21

What muscles prevent scapula lateral translation?

Answer 21

The axioscapular muscles, namely trapezius and rhomboids

Question 22

What do the anterior and mid deltoid do that requires high rotator cuff compressive force to maintain stability?

Answer 22

High superior translation force produced by ant and mid delt requires high rc compressive force to maintain stability, especially during outstretch distal arm position in prone creating longer lever arm