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Guest Post: PT Noriko Yamaguchi on shoulder health and rehab

Updated: Feb 7

Shoulder anatomy and function – balancing stability with mobility

The shoulder girdle refers to a complex of three synovial joints, plus an extra muscular attachment of the shoulder blade (scapula) on the rib cage (thorax), which I will refer to as the scapulothoracic joint.

- Sternoclavicular joint (SCJ) – attaches the clavicle (collarbone) to the sternum (breast bone)

- Acromioclavicular joint (ACJ) – attaches the clavicle to the acromion (outer tip of the shoulder blade)

- Glenohumeral joint (GHJ) – attaches the humerus (upper arm) to the scapula. This joint is the “shoulder joint”

Mobility is required at each of these joints when we move our arm, and multiple muscle groups are engaged along the scapula and shoulder to allow movement in all three planes of motion. In addition, your postural muscles in the trunk automatically engage to create stability through your core before you even initiate lifting of your arm. As you can hopefully appreciate, upper body movement is a dynamic coordination of many moving parts, with certain parts creating stability in order to allow other parts to move with efficiency and precision. With so many degrees of freedom in our shoulders and with the coordination of so many moving parts, it’s no wonder that many people experience shoulder pain or injury at some point in their lives!

The SCJ has the least movement of the shoulder girdle due to strong ligaments holding the clavicle to the sternum. The ACJ has non-perceptible but important mobility during shoulder movements, especially as the arm raises overhead. What we appreciate and see as “shoulder range of motion” is a composite of movement at the GHJ and the scapulothoracic joint. About 2/3 of the motion of raising your arm overhead comes from the GHJ and the other 1/3 comes from the scapulothoracic joint. The coordination of this movement is referred to as scapulohumeral rhythm, and the amount and timing of movement is key to efficient and biomechanically sound shoulder motion.

The GHJ is a shallow ball-and-socket joint, where the socket (the glenoid fossa) sits roughly perpendicular to the ground, kind of like a parenthesis shape. In order for the ball (the humeral head) to stay in a shallow socket, we have cartilage (the glenoid labrum) to create a little more of a cup to the socket for better surface area, and we have four rotator cuff muscles to stabilize the ball in the socket. Both the glenoid labrum and the rotator cuff are prone to excess wear and tear when we repeatedly move our shoulder with sub-optimal scapulohumeral rhythm due to muscle weakness or inflexibility, joint stiffness, or poor movement coordination.

Shoulder Injuries

Injuries can occur due to trauma, such as a fracture or dislocation after a fall. Injuries can also occur when we place more demand on the joints/muscles than what they can actually tolerate (for example, returning to sport too early after an injury and then re-injuring yourself). Frequently, shoulder pain occurs as a result of chronic, repetitive overuse, when extra wear and tear on the shoulder girdle finally catches up with you. Most of these injuries are caused by inflammation from small micro-tears that never have enough time to heal, which can lead to the tissues being in a chronic inflammatory state. These diagnoses typically are named by the tissue structure and end in “-itis” (i.e. inflammation), for example bursitis (inflammation of the bursa) or tendonitis (inflammation of the tendon).

Overuse injuries often occur due to over-training (such as progressing too fast and too soon, or not allowing adequate rest/recovery time). Additionally, underlying mobility, stability, and/or coordination impairment causing inefficient, sub-optimal movement can make people at higher risk for developing overuse injuries. Recovery from overuse injuries require both time for the tissues to heal AND addressing any movement impairments that may have predisposed you the injury.

Common impairments at the shoulder include:

  • Poor initial postural alignment of the shoulder girdle

  • Inadequate flexibility of the pectoralis muscles, the latissimus dorsi, the posterior rotator cuff muscles (infraspinatus and teres minor)

  • Joint stiffness at the ACJ, GHJ, scapulothoracic joint, or thoracic spine

  • Muscle weakness in the scapular stabilizers (serratus anterior, middle and lower trapezius, rhomboids)

  • Muscle coordination problems causing poor scapulohumeral rhythm – typically due to weakness in certain muscles and over-reliance on other muscles to compensate for weakness.

These impairments are often inter-related, and so generic “shoulder physical therapy” often takes the shotgun approach of giving you a lot of different things to target each of these areas. My preference is to take a more individualized approach and determine what primary impairments need to be addressed first and/or more aggressively in order for the other impairments to improve.

When do I see a PT?

In Oregon, the public can go directly to a physical therapist for any pain or mobility impairment without having to get a referral from your MD. However, most medical insurance companies require a medical referral for them to cover physical therapy services, and they will only pay for physical therapy in the context of physical rehabilitation, not injury prevention.

I personally believe that real health care should be about staying injury free, not waiting until you have a problem! With prevention and physical well being in mind, my preference is to have all individuals have a baseline functional and mobility assessment from their physical therapist. Just like how you have a general physical exam by your primary care physician every year to help you manage and maintain your health, your physical therapist should be the person in your health care team that helps you monitor, manage, and maintain your physical strength, endurance, and mobility. They should work with your trainer/coach and adjust your exercise program (think of exercise is healthy medicine!) to help you reach your health and fitness goals. The great thing about this model is that if you DO get injured, we already have baseline, pre-injury measures of your physical mobility & performance to compare your injured state against, which then allows us to better individualize your recovery plan.


I’m Noriko, and I am the founder and owner of Trifecta Physical Therapy, which is a mobile practice that provides private physical rehabilitation, strength and conditioning, and wellness services to your home, office, or other location of your choosing. My mission is to optimize how you feel and how your body performs by integrating human anatomy & physiology, biomechanics, and principles of physical rehabilitation into your training and health maintenance program.

As a Doctor of Physical Therapy, I am trained in the evaluation of movement-related impairment and dysfunction and in physical rehabilitation to improve function and quality of life. I have clinical experience in orthopedic, sports, neurologic, and oncology rehabilitation, and my strength as a clinician is my ability to integrate the evaluation and intervention techniques of all branches of physical therapy to create an individualized program for each patient. I am also a Certified Strength and Conditioning Specialist (CSCS) through the National Strength and Conditioning Association (NSCA). In addition to extensive clinical and teaching experience in the area of therapeutic exercise, I have worked with recreational and competitive athletes to develop training programs as they transition from rehabilitation to return to sport.

Regardless of your injury or health condition, current level of function and fitness, past medical and social history, or body size and shape, I believe all of us can experience the joy of physical well-being. Find me at!

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