Muscle Insertion

Diagram of the latissimus dorsi muscle on the skeleton.
Diagram of the latissimus dorsi muscle on the skeleton. SCIEPRO/Science Photo Library/Getty Images

Muscle Insertion

The insertion of the muscle is the end of the muscle attaching to the freely moving bone of its joint. To understand muscles and joint movements, there are four things to keep in mind:

  • Movement happens at joints, with one bone of the joint moving freely while the other remains relatively stationary.

    Muscle attachments are named with this in mind, which means the place of insertion is usually the part of the joint that does the moving.

    But depending on your position, it's possible for the bone on the insertion end of the joint being moved to provide the stability, thereby allowing the bone that is usually stable to be the one that moves about. (The Pilates method takes advantage of this fact in the design of exercises that work your "anti-gravity" muscles.)
  • Muscles are power engines for movement; they attach to bone on either end(s) of a joint, crossing the joint space as they do.
  • The part of the muscle located between 2 ends is known as the belly of the muscle.
  • All of this is significant because the size, direction and shape of the muscle and muscle attachments are part of what determines the range of motion of the joint, and therefore flexibility.

Back Muscle Insertions - Examples

Let's take a few examples from your neck and back muscles.

Insertion of the Sternocleidomastoid Muscle, or SCM

One prominent muscle in the neck is the sternocleidomastoid, or SCM, for short. This muscle runs diagonally from your skull to your breastbone and collarbone. Its job is mainly to turn and tilt your head, but it also plays assistive roles in bending and extending your head.

The SCM insertion is located on a small tag of bone just behind your ear. This tag of bone is called the mastoid process, aptly enough.

(Feel free to touch behind your ear, towards the bottom to feel your mastoid process.)

In case you're interested, the origin of the SCM, i.e., the normally stable end of this muscle, and the end opposite to the insertion, actually divides into two parts, with each attaching on different, but nearby areas.

These parts are called "heads." One head attaches, or as it is in this case, originates on the top of the collarbone, close to the center of your body. The other head originates at the outside surface of the top of your breastbone.

Insertion of the Latissimus Dorsi Muscle, or the "Lats"

Next, let's look at the latissimus dorsi muscle. This is a very large back muscle that spans mainly from the area around your hips and back and goes all the way to your upper extremity. Despite its size, the latissimus dorsi muscle eventually tapers to a point that inserts on the inside of your humerus, which is the bone of your upper arm.

Source

Kendall, Florence Peterson, McCreary, Elizabeth Kendall, and Provance, Patricia Geise. Muscles Testing and Function with Posture and Pain. 3rd. Baltimore, Maryland: Williams & Wilkins, 1983.

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