What Does the Trapezius Muscle Do?

Trapezius performs several functions that include stabilization and movement of the shoulder blade or scapula, maintain posture, and enabling movements.

The trapezius is a large superficial back muscle that resembles a trapezoid in shape. It is broad, triangular, and runs at the back of the neck and upper trunk. It starts at the base of the skull and spreads downwards towards the middle of the back and the shoulder blades (scapulae). There are separate trapezius muscles for the left and right sides of the body. The muscle has three groups of muscle fibers: upper, middle, and lower groups. Trapezius performs several functions that include:

  • Stabilization and movement of the shoulder blade or scapula, which is necessary for performing tasks like throwing objects.
  • Maintaining posture
  • Enabling movements, such as side bending, rotating the arm inwards, elevating and depressing the shoulders, and turning the head.

The muscle is supplied by the eleventh cranial nerve called the spinal accessory nerve. An injury to this nerve can lead to the paralysis of the trapezius muscle. This is tested by asking the patient to shrug their shoulders, first without resistance and then with the doctor applying resistance to the shoulders.

Can trapezius muscle cause headaches?

Trapezius muscle spasticity may cause tension headaches. The spinal accessory and occipital nerves pass through this muscle. Spasms or increased tone of trapezius can put pressure on these nerves causing a headache. The headache has a typical ‘ram's horn’ distribution causing throbbing pain on both sides of the head, traveling from the region at the back of the head and wrapping around to the top of the head and forehead region. This type of headache is exacerbated by stress, bad posture, and lack of proper stretching before any activity. Unlike migraine, tension headache is not preceded by an aura or prodrome, such as intolerance to light and sound, seeing flashes of light, or strange smells.
Tension headache may be treated with physical therapy, stretching, stress and anxiety-relieving activities, and NSAIDs (nonsteroidal anti-inflammatory drugs).

What is a trapezius strain?

A trapezius strain refers to the stretching or tearing of the trapezius muscle fibers. Trapezius muscle strain is a common injury that may result when the muscle is excessively stretched or forced to contract too strongly. This may limit the range of motion and decrease the strength in the arms and shoulders. Depending on the severity of the injury, trapezius muscle strain may be:

  • Grade I strain: This is a mild form of strain that involves stretching or injury of only a few muscle fibers. There is often pain and tenderness in the affected area, but the muscle strength remains normal. A grade I strain generally heals with a few weeks.
  • Grade II strain: This results due to injury to a larger number of muscle fibers. It manifests as pain and tenderness, which are more severe than a grade I strain along with some loss of muscle strength. There may also be bruising and swelling at the affected site. A grade II strain may take a few months to heal.
  • Grade III strain: This is the most severe type of strain that often needs surgical repair. It leads to the complete ripping apart of the trapezius muscle. This may cause severe pain, tenderness, swelling, and change in the color of the affected area. The tear of the muscle can cause a visible gap or dent under the skin where the injured pieces of muscle are separated.


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Ourieff J, Scheckel B, Agarwal A. Anatomy, Back, Trapezius. StatPearls Publishing; 2020. Harvard Health Publishing. Muscle Strain. December, 2018.