The trapezius is a three-part (tripartite) muscle of the upper back extending from the base of the skull all the way to the lower thoracic spine and laterally from the clavicle to the entire length of the spine of the scapula. Together the two trapezii form a diamond or kite-shaped trapezoid from which the muscle derives its name.
Although usually discussed as one muscle, it is separated into distinct groups of fibers which run in different directions and thus can have slightly different movement roles. These different groups of fibers are usually referred to as the upper, middle, and lower trapezius. Some experts divide the middle section into two parts, the upper middle and lower middle but for the purposes of this article, which is to serve as an introduction for the trapezius trigger point explanation, we will consider only three divisions.
In general, the action of the trapezius is to elevate and depress the scapula and to rotate the shoulder girdle upward and downwards. The trapezius also extends the head and when all the fibers work together they tend to pull the shoulder upward and adduct the scapula. Adduction of the scapula is the same thing as “retraction” of the scapula and means to move the scapula medially toward the spinal column.
The trapezius fixes the scapula for movement of the shoulder joint and continuously rotates the scapula upward to permit the arm to be raised over the head. The trapezius is most well-known as the “shrug” muscle and it is worked heavily with the traditional bodybuilding shrug exercise as well as during the Olympic lifts and anything that elevates the shoulders. More specific functions of the upper, lower, and middle fibers will be discussed below under “actions”.
The trapezius is sometimes considered an “upper back” muscle or a “shoulder” muscle but it is more correctly considered a muscle of the scapulothoracic joint of the shoulder girdle (The two other shoulder girdle joints are the sternoclavicular (SC) and the acromioclavicular joint [AC]). The action of the trapezius is closely linked with the levator scapulae in shoulder elevation and its other synergists in this role are the rhomboids major and minor. Other trapezius muscle relationships are shown in the table below.
The upper trapezius was found by Travell and Simons to be the muscle most often affected by trigger points, which has been confirmed by other authors. The closely related levator scapulae were also found to be the top runner in some studies and this would make sense because the same perpetuating circumstances that affect the trapezius would also affect the levator scapulae. 1Simons, David G., Janet G. Travell, Lois S. Simons, and Janet G. Travell. “Chp. 8: Masseter Muscle.” Travell & Simons’ Myofascial Pain and Dysfunction: the Trigger Point Manual. Baltimore: Williams & Wilkins, 1999. 329. Print.
Trapezius Synergists and Antagonists Muscles by Shoulder Girdle Action
|Trapezius (Upper Fibers)||Trapezius (Lower Fibers)|
|Rhomboid Major||Pectoralis Minor|
|Abduction (Protraction)||Adduction (Retraction)|
|Serratus Anterior||Trapezius (Middle Fibers)|
|Pectoralis Minor||Rhomboid Major|
|Upward Rotation||Downward Rotation|
|Trapezius (Upper &Lower Fibers)||Rhomboid Major|
|Serratus Anterior||Rhomboid Minor|
Trapezius Origin, Insertion, and Actions
Origin: Upper fibers: base of skull at occipital protuberance and the nuchal ligaments (ligamentum nuchae) of neck. Middle fibers: spinous processes of seventh cervical vertebra and upper three thoracic vertebrae. Lower fibers: spinous processes of fourth through twelfth thoracic vertebrae.
The upper (superior) fibers proceed from their origin downward and laterally. The middle fibers run laterally to toward the acromion process and the lower (inferior) fibers run upward and laterally.
Insertion: Upper fibers: posterior aspect of the lateral third of the clavicle. Middle fibers: medial border of acromion process and superior lip of the posterior border of the spine of the scapula. Lower fibers: tubercle at the apex smooth triangular surface at base of scapular spine via an aponeurosis.
Action: Upper fibers: elevation and adduction of the shoulder girdle; extension of the head. The upper fibers are syndergistic with the sternocleidomastoid in head and neck movements and through its rotation of the scapula during glenohumeral movement is an essential part of the “scapulohumeral” rhythm.
Middle Fibers: elevation, upward rotation and adduction of the scapula. By helping to stabilize the scapula these fibers aid in the elevation of the arm.
Lower fibers: depression and adduction of the scapula.
Both sides of the trapezius work together during extension of the head, neck and thoracic spine and during any symmetrical lifting activity such as overhead pressing. 2Behnke, Robert S. Kinetic Anatomy. Champaign, IL: Human Kinetics, 2001. Print.,3Floyd, R. T., and Clem W. Thompson. Manual of Structural Kinesiology. Dubuque, IA: WCB/McGraw-Hill, 1998. Print.
Sources [ + ]
|1.||↲||Simons, David G., Janet G. Travell, Lois S. Simons, and Janet G. Travell. “Chp. 8: Masseter Muscle.” Travell & Simons’ Myofascial Pain and Dysfunction: the Trigger Point Manual. Baltimore: Williams & Wilkins, 1999. 329. Print.|
|2.||↲||Behnke, Robert S. Kinetic Anatomy. Champaign, IL: Human Kinetics, 2001. Print.|
|3.||↲||Floyd, R. T., and Clem W. Thompson. Manual of Structural Kinesiology. Dubuque, IA: WCB/McGraw-Hill, 1998. Print.|