What is the Action of the Trapezius Muscle?

Man flexing his back and arm muscles
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The trapezius muscle may be best known as a source of stiffness across the top of the shoulders. It frequently becomes tight and contracted if you sit for long hours at a desk. However, the trapezius, which covers a broad area of the back of your neck and upper back, serves multiple functions. It helps to move and stabilize your shoulder blade in many common actions, such as shrugging the shoulders, pulling the shoulders back and raising the arms overhead.

Trapezius Actions

The trapezius originates from the back of the base of the skull and the cervical and thoracic vertebrae. It wraps around the neck and ribcage to insert onto the outer part of the collarbone and the shoulder blade. The trapezius can be divided into three sections -- upper, middle and lower -- each of which has a different function. The upper part is responsible for elevating, or shrugging, the shoulders. If the shoulders are fixed, the upper trapezius muscles extend the neck, tilting the head up. Contracting the upper trapezius on just one side will tilt the head to that side while rotating it in the opposite direction. The middle portion of the muscle retracts the shoulder blade, pulling it closer to the spine, while the lower trapezius depresses the shoulder blade, drawing it down and in toward the spine.

Upward Rotation

The upper and lower portions of the trapezius also act to upwardly rotate the shoulder blade, in concert with a muscle on the side of the ribcage called the serratus interior. Upward rotation serves to face the shoulder socket, located on the outer shoulder blade, toward the ceiling. This action is necessary to reach your arms overhead. Without sufficient upward rotation of the shoulder blade, your upper arm bone would become pinched against part of the shoulder blade known as the acromion -- with the potential for shoulder injury.

Strengthening the Trapezius

Exercises such as shrugs work the upper trapezius muscle. Rowing exercises, such as bent over rows and seated rows, target the middle portion. Overhead pulling exercises, including pull-ups, chin-ups and pull-downs, strengthen the lower section. Because it is common for many people to have a stronger upper than lower trapezious, incorporating exercises for the middle and lower parts into your workout can help maintain healthy alignment of the shoulders.

Stretching the Trapezius

To stretch your upper trapezius, stand and bring your right arm behind your back. Pull your wrist with your left hand and tilt your head to the left. Repeat with your left arm behind your back. To stretch the middle and lower parts, cross your right arm across your chest. Pull your elbow toward your chest with your left hand. Before beginning a stretching routine, warm up with light aerobic exercise, including dynamic movements of your arms and shoulders. Hold stretches for 10 to 30 seconds and repeat two to four times. Stretch only to the point of tightness -- not to the point of pain.