Shoulder Complex Muscle Analysis
1. Lie prone on a table with your right arm hanging over the side of the table holding a weight in your right hand. Using only shoulder girdle motion and no shoulder joint motion, pull the weight straight up from the floor.
a. What join action is occurring at the shoulder girdle?
b. What muscles are prime movers of this action?
c. Is this an open-chained or closed-chained activity?
2. Lie in the same position, holding a weight, move your arm up and out by doing shoulder horizontal abduction.
a. What shoulder girdle motion is accompanying shoulder horizontal abduction?
b. What muscles are the prime movers in this shoulder girdle motion?
c. Is this a concentric, eccentric, or isometric contraction?
3. Using a lat pull down machine reach up and grasp the handles. Pull-down while keeping your arms moving in the frontal plane.
a. What shoulder girdle motions are accompanying shoulder adduction and lateral rotation?
b. What muscles are the prime movers in these shoulder girdle motions?
c. Is this a concentric or eccentric activity?
Sample Solution
a. The joint action occurring at the shoulder girdle is known as scapular elevation, which involves retracting and upwardly rotating the shoulder blades (Levangie & Norkin, 2020).
b. The primary muscles involved in this action are the trapezius (upper fibers), rhomboids (major/minor) and serratus anterior (Williams et al., 2015). These muscles work together to elevate and rotate the scapulae while keeping it stabilized during movement.
c. This activity would be classified as an open-chain exercise since the movement is not constrained by any fixed point; instead, it relies on muscular contraction to move through its full range of motion with no external resistance other than that provided by gravity or a weight held in one hand (Van Mechelen et al., 1992).
Overall then, it can be seen that when performing scapular elevation with a weight, various muscle groups work together to lift and stabilize the shoulder blades against gravity – resulting in an open-chained exercise which provides benefits for both muscle strength and joint stability.
