Shoulder- Part 2- Kinetics

Question 1

In shoulder abduction, which muscles drive initial 30 degrees of ST motion?

Answer 1

Upper trapezius (also serratus anterior pulls scapula down)

Question 2

Where is the axis of rotation for initial 30 degrees of ST motion?

Answer 2

Axis is through SC joint and functionally goes through the root of spine of scapula

Question 3

In shoulder abduction, which muscles drive the later 30 degrees of ST motion?

Answer 3

Middle and Lower trapezius

Question 4

Where is the axis of rotation for the later 30 degrees of ST motion?

Answer 4

Axis and motion in AC joint. As axis moves the function of the lower trap becomes different

Question 5

Force couple

Answer 5

two or more muscles simultaneously produce forces in different linear directions, although the resulting torques act in the same rotary direction

Question 6

What frontal plan motion at the GHJ would be effected if the deltoid acted alone and unopposed?

Answer 6

It would move up (abduct) because there would be more translation than rotation

Question 7

What frontal plan motion at the GHJ would be effected if the infraspinatus, teres minor, and subscapularus acted alone and unopposed?

Answer 7

The humeral head would be pushed into the glenoid fossa because there would be more rotation than translation

Question 8

How do the combined actions of the rotator cuff and the deltoid produce motion at the GHJ

Answer 8

The translations cancel each other out and the rotation work together to combine and create mostly rotational component

Question 9

What frontal plan motion at the GHJ would be effected if the supraspinatus acted alone and unopposed?

Answer 9

I would pull the head of the humerus in, larger rotational component.

Question 10

What does gravity do when working with the supraspinatus during elevation

Answer 10

gravity helps take out the translational components, when added all together upward translation wins out just a little

Question 11

Osteokinematic motion that bicep brachii contributes to in arm elevation

Answer 11

Flexion because it runs more anteriorly. Bowstring effect, it stabilizes shoulder anterior and has a really strong bowstring effect.

Question 12

Length tension relationship in the deltoid through arm elevation

Answer 12

It is maintained because the scapula continues to move as the humerus moves and shortens the muscle the scapula moves and lengthens it.

Question 13

Trapezius is more critical for which plane of motion?

Answer 13

Frontal plane- it is the first to elevate the scapula and it lays in the frontal plane

Question 14

Serratus anterior is more critical for which plane of motion?

Answer 14

Sagittal plane- lays more in sagittal plane, more critical roll in scapula retraction.

The clinical significance of this is that we must be able to elevate arm in both planes so need muscles in both to assist us

Question 15

Motion at the ST joint produced by the latissimus dorsi in open chain vs. closed chain

Answer 15

• Open chain: Depression and downward rotation

- Closed chain: Thorax goes up and moves under scapula

Question 16

Role of rhomboids during add and ext from a abd and flex position at the GHJ

Answer 16

Rhomboids: retract, downward rotate, and elevate scapula

They work as a large stabilizer and allow the GHJ to really move and maintain function

Question 17

What is the difference in strength for internal vs. external rotators and why?

Answer 17

IR are stronger because of larger muscle mass, number of muscles doesn’t matter overall compared to mass of muscle

Question 18

Problem with different strength between IR and ER muscles

Answer 18

The ERs tear because they aren’t strong enough to slow down IRs.
Think of over head throwing athletes, in this case ERs are also functioning eccentrically which must produce a stronger force

Question 19

Primary IR

Answer 19

Subscapularis, anterior deltoid, pectoralis major, lattisimus dorsii, and teres major

Question 20

Primary ER

Answer 20

Infraspinatus, teres minor, and posterior deltoid