Arm Care Science: The Trapezius
To truly understand the driving forces in Arm Care Science we need to understand the critical function of the Trapezius muscle. The trapezius is sectioned into the upper, middle and lower parts of this large muscle. It is a triangular flat muscle of the shoulder girdle. Its extensive origin starts at the base of the skull and continues to the upper lumbar vertebrae and inserts on the lateral aspect of the clavicle, acromion and scapular spine. It is innervated by the spinal accessory nerve.
The upper trap or descending, superior part runs from the occipital bone and nuchal ligament to lateral third of the clavicle. The middle or transverse trap originates from the spinal processes of the first to fourth thoracic vertebrae and inserts at the acromion. The lower or ascending, inferior trap extends from the spinal processes of the fifth to twelfth thoracic vertebrae to the scapular spine. (Terry, & Chopp, 2000).
Arm Care Science: Function of Trapezius
The purpose of the trapezius muscle is to support posture and active movement which is the foundation of Arm Care Science. The trapezius supports posture working as a stabilizer to secure the shoulder blade at the thorax. The movements it is responsible for is to tilt and turn the head and neck. It can also shrug and steady the shoulders while also twisting the arms. The anatomical movements it can create is elevation, depression, retraction and assists in upward rotation of the scapula.
The descending or upper part of the trapezius specifically causes elevation and retraction of the clavicle as it does not attach directly to the scapula while the ascending or lower part depresses. Furthermore, a unilateral contraction bends the head to the ipsilateral side, known as lateral flexion, whereas a bilateral contraction raises the head and the cervical vertebral column, known as dorsal flexion. The middle trapezius directed medially has only a small moment arm for upward rotation and is subsequently likely most active to offset lateral translation from the serratus anterior. A good example of this would be after a throwing athlete releases the ball the scapula is being distracted in a lateral direction. Preventing this movement is a core principle in Arm Care Science.
The lower trapezius assists in medial stabilization and upward rotation of the scapula. Subsequently, the lower trapezius is the only component of the trapezius that can substantively upwardly rotate the scapula (Phadke, Camargo, & Ludewig, 2010). Upward rotation of scapula is critical for protecting the rotator cuff when throwing a baseball. This is another core principle of Arm Care Science. However, its relative moment arm of the lower trapezius will change across the range of motion for arm elevation.
The appropriate force couples for scapular stabilization include the upper and lower portions of the trapezius muscle working together with the rhomboid muscles, paired with the serratus anterior muscle (Kibler, 1998). The appropriate force couples for acromial elevation are the lower trapezius and the serratus anterior muscles working together paired with the upper trapezius and rhomboid muscles. Muscles are noted to act in different parts of the force couples depending on the activity requirements.
The common mechanics of lifting the arm over the head is highly dependent on the trapezius muscle along with the serratus anterior. During the first 30° to 50° of glenohumeral abduction, the scapula moves laterally with the support of the upper and lower trapezius. The next 65° of abduction the scapula rotates on a fixed axis until it reaches full elevation once again supported by the upper and lower trapezius. This motion accounts for a 2:1 ratio between glenohumeral abduction and scapulothoracic rotation. If the scapula fails to rotate and elevate through this 2:1 ratio then this could potentially lead to injury especially in throwing athletes.
Arm Care Science: Dsyfunction of the Trapezius
The common pathomechanics that occur from dysfunction of the trapezius muscle is shoulder impingements. This defines the failure of Arm Care Science. This is the result of decreased activation of the middle or lower serratus anterior and rotator cuff, delayed activation of the middle and lower trapezius, and increased activation of the upper trapezius and middle deltoid. The serratus anterior and especially the lower trapezius muscles appear to be the first muscles involved in inhibition-based muscle dysfunction (Glousman et al., 1998) Lack of acromial elevation and consequent secondary impingement can be seen early in many shoulder problems, such as rotator cuff tendinitis and glenohumeral instability, and can play a major role in defining the clinical problems that are associated with these diagnostic entities (Jobe, Kvitne, & Giangarra, 1989).
Muscle inhibition or weakness is common in glenohumeral abnormalities, whether from instability, labral lesions, or arthrosis (Bagg, & Forrest, 1986). It seems that the lower trapezius and the serratus anterior muscles are linked to the beginning of shoulder abnormalities. Muscle inhibition, and resulting scapular instability appears to be a nonspecific response to a painful condition in the shoulder rather than a specific response to a certain glenohumeral pathologic situation. Evidence supports this claim with the findings of scapular instability in as many as 68% of rotator cuff problems and 100% of glenohumeral instability problems (Kuhn, Plancher, & Hawkins, 1995). Inhibition is defined as a decreased ability for the muscles to exert torque and stabilize the scapula and as a disorganization of the normal muscle firing patterns of the muscles around the shoulder.
Evidence suggests that an overactive or tight upper trapezius and a weak and inactive lower trapezius has a strong correlation to injury (Smith, Sparkes, Busse, & Enright, 2009). In this study, asymptomatic subjects had an upper trapezius to lower trapezius ratio of 1.80. Symptomatic subjects had an upper trapezius to lower trapezius ratio of 3.15. What this means is that the upper trapezius is a little more than 3 times more active than the lower trapezius during scapular plane elevation in patients with subacromial impingement.
The most common problem I have dealt with in my practice of Arm Care Science is scapular dysfunction in baseball pitchers that usually leads to pain in the overhand throwing position. This pain usually occurs during the moment of maximum external rotation of the humerus and around 90-100 degrees of shoulder abduction. In most cases, the pain is remedied when I prescribe exercises to smash, stretch and strengthen the serratus anterior and the lower trapezius. I find it effective to first smash or foam roll the serratus anterior and the upper and lower trapezius. This helps to create more freedom of movement by lengthening the fascia that could be inhibiting the muscle. I then follow the smashing of the muscle with stretching to continue the process of lengthening the fascia. Once the muscle is moving freely and without pain or restriction, I then use exercises to strengthen the muscle functions. In most cases, this will remedy the pain and within a few weeks, the athlete can go back to high-intensity throwing.
Arm Care Science Reference
Bagg, S. D., & Forrest, W. J. (1986). Electromyographic study of the scapular rotators during arm abduction in the scapular plane. American Journal of Physical Medicine & Rehabilitation, 65(3), 111-24.
Glousman, R., Jobe, F., Tibone, J., Moynes, D., Antonelli, D., & Perry, J. (1988). Dynamic electromyographic analysis of the throwing shoulder with glenohumeral instability. The Journal of Bone and Joint Surgery, 70(2), 220-6.
Jobe, F. W., Kvitne, R. S., & Giangarra, C. E. (1989). Shoulder pain in the overhand or throwing athlete. The relationship of anterior instability and rotator cuff impingement. Orthopedic Reviews, 18(9), 963-75.
Kibler, W. B. (1998). The role of the scapula in athletic shoulder function. American Journal of Sports Medicine, 26(2), 325-37.
Kuhn, J. E., Plancher, K. D., & Hawkins, R. J. (1995). Scapular Winging. Journal of the American Academy of Orthopaedic Surgeons, 3(6), 319-325.
Phadke, V., Camargo, P. R. & Ludewig, P. M., (2010). Scapular and rotator cuff muscle activity during arm elevation: A review of normal function and alterations with shoulder impingement. Rev Bras Fisioter, 13(1), 1-9.
Smith, M., Sparkes, V., Busse, M., & Enright, S. (2009). Upper and lower trapezius muscle activity in subjects with subacromial impingement symptoms: is there imbalance and can taping change it? Physical Therapy in Sport, 10(2), 45-50.
Terry, G. C., & Chopp, T. M., (2000). Functional Anatomy of the Shoulder. Journal of Athletic Training, 35(3), 248-255.