Functional Roles of the RC & Axioscapular muscles

Question 1

In what ways does the RC provide dynamic stability at the GHJ?

Answer 1

• Taking up the slack in the shoulder joint capsule during movement
• Provides a medial force of the Humeral Head to accurately position it within the centre of the glenoid fossa during movement
• Prevents the deltoid from gliding the humeral head superiorly

Question 2

During maximum isometric abduction at the GHJ, how does the RC work?

Answer 2

Anterior cuff and posterior cuff co-contract to:
- globally compress the shoulder joint
- counterbalance the superior translation of the humeral head

Question 3

During isometric and dynamic flexion OR extension does the RC co-contract?

Answer 3

No they dont co-contract at similar levels.

During these form of contractions the RC is active at higher levels on the opposite side to the muscle producing the movement.

Therefore the anterior cuff is more active during shoulder extension and vice versa

Question 4

What is the relationship between the scapula and the clavicle?

Answer 4

Clavicle provides passive stability of the scapula

During upwards rotation of the scapula, the clavicle is rotated posterior due to tension of the conoid ligament

Question 5

Does the humerus internally or externally rotate during Abduction/flexion?
Explain why?

Answer 5

The humerus externally rotates

WHY?
ER allows the greater tubercle to clear the coracoacromial arch (prevents it hitting the acromion)

Question 6

Ratio of humerus to scapula movement during:
1) 0-30 degrees abduction
2) 30-180 degrees abduction

Answer 6

1) mainly humerus movement –> 4:1 Ratio

2) approx. 1.5 humerus movement to scapula movement

Question 7

Humerus VS scapula movement during:
1) 0-60 degrees flexion
2) 60-180 degrees flexion

Answer 7

1) mainly humerus movement
2) approx equal humerus to scapula movement

Question 8

Does load influence shoulder muscle recruitment pattern?

Answer 8

NO!

• Load doesnt change the recruitment pattern
• recruitment patterns are established at low loads
  –> as you increase load, there is an increase in activity of all the muscle in the same systematic fashion

FOUNDATIONS SHOULD BE SET AT LOW LOADS TO ENSURE CORRECT ACTIVITY BEFORE AN INCREASED LOAD IS APPLIED

Question 9

Do shoulder exercises target specific shoulder movers?

Answer 9

NO! NO! NO! DO NOT EVER IMPLY THIS

All shoulder muscles will be active to a certain degree due to their stabilising roles to ensure for an effective movement at the shoulder joint

Question 10

How do you teach a muscle to learn their stabilising function?

Answer 10

By working muscles that cause the destabilising of the scapula / joint

–> their force as stabilisers has to counterbalance the force against the destabilising force created by the alternate shoulder muscles