Shoulder- Part 2- Kinetics Flashcards
(20 cards)
In shoulder abduction, which muscles drive initial 30 degrees of ST motion?
Upper trapezius (also serratus anterior pulls scapula down)
Where is the axis of rotation for initial 30 degrees of ST motion?
Axis is through SC joint and functionally goes through the root of spine of scapula
In shoulder abduction, which muscles drive the later 30 degrees of ST motion?
Middle and Lower trapezius
Where is the axis of rotation for the later 30 degrees of ST motion?
Axis and motion in AC joint. As axis moves the function of the lower trap becomes different
Force couple
two or more muscles simultaneously produce forces in different linear directions, although the resulting torques act in the same rotary direction
What frontal plan motion at the GHJ would be effected if the deltoid acted alone and unopposed?
It would move up (abduct) because there would be more translation than rotation
What frontal plan motion at the GHJ would be effected if the infraspinatus, teres minor, and subscapularus acted alone and unopposed?
The humeral head would be pushed into the glenoid fossa because there would be more rotation than translation
How do the combined actions of the rotator cuff and the deltoid produce motion at the GHJ
The translations cancel each other out and the rotation work together to combine and create mostly rotational component
What frontal plan motion at the GHJ would be effected if the supraspinatus acted alone and unopposed?
I would pull the head of the humerus in, larger rotational component.
What does gravity do when working with the supraspinatus during elevation
gravity helps take out the translational components, when added all together upward translation wins out just a little
Osteokinematic motion that bicep brachii contributes to in arm elevation
Flexion because it runs more anteriorly. Bowstring effect, it stabilizes shoulder anterior and has a really strong bowstring effect.
Length tension relationship in the deltoid through arm elevation
It is maintained because the scapula continues to move as the humerus moves and shortens the muscle the scapula moves and lengthens it.
Trapezius is more critical for which plane of motion?
Frontal plane- it is the first to elevate the scapula and it lays in the frontal plane
Serratus anterior is more critical for which plane of motion?
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
Motion at the ST joint produced by the latissimus dorsi in open chain vs. closed chain
- Open chain: Depression and downward rotation
- Closed chain: Thorax goes up and moves under scapula
Role of rhomboids during add and ext from a abd and flex position at the GHJ
Rhomboids: retract, downward rotate, and elevate scapula
They work as a large stabilizer and allow the GHJ to really move and maintain function
What is the difference in strength for internal vs. external rotators and why?
IR are stronger because of larger muscle mass, number of muscles doesn’t matter overall compared to mass of muscle
Problem with different strength between IR and ER muscles
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
Primary IR
Subscapularis, anterior deltoid, pectoralis major, lattisimus dorsii, and teres major
Primary ER
Infraspinatus, teres minor, and posterior deltoid
