Unlike the hip joint, where the head of the femur (thigh bone) fits snugly into the hip socket (acetabulum), the humerus (upper arm bone) has a relatively loose fit into the shoulder joint. Although this loose fit gives a wide, varied range of motion, the shoulder joint is susceptible to injury. Balancing the action of the muscles surrounding the shoulder joint can help prevent or heal conditions such as rotator cuff tears, osteoarthritis, shoulder impingement, and shoulder tendonitis.
The basic principle to balance the muscular action of any area of the body is to concentrically engage a phasic muscle and then eccentrically lengthen an opposing postural muscle. (For a discussion of concentric and eccentric engagements see blog #3; for a discussion of phasic and postural muscles see blog #2.)
Applying the "Balanced Muscular Action Principle" to the shoulders requires three groups of muscles, thus three sets of instructions:
Instruction #1- Concentrically engage the muscles between the shoulder blades (rhomboids), then eccentrically lengthen the chest muscles (pectoral major). These actions broaden the front of the chest, as they retract the head of the arm bone (humerus).
Instruction #2- Concentrically engage the large back muscle (trapezius) from the top of the shoulder blades (scapula) to the bottom of the posterior rib cage at T12, then eccentrically lengthen the pectoral minor (top of the chest) from the third rib to the coracoid process at the front top of the scapula. These actions take the shoulder blades down the back and open the top of the chest.
Instruction #3- Concentrically engage the posterior deltoid and the posterior rotator cuff muscles (infraspinatus and teres minor), then eccentrically lengthen the lats (latissimus dorsi). The lats can be eccentrically lengthened by externally rotating the upper arm bones from the inner tricep to the inner bicep. When the lats are too strong relative to the posterior shoulder muscles, the shoulder tends to roll forward and puts the joint at risk.
Learning to isolate these muscle groups may require time and persistence, but the benefits in prevention, healing, and alignment are worth the effort.
Stay Tuned! Next Blog: Lower Leg and Foot