Muscle Insertion and Your Joints

A muscle attaches at either the muscle origin or the muscle insertion. The insertion of a muscle is defined as the place where one end of a muscle is attached to the freely moving bone of its joint.

To understand muscle and joint movements, there are four things to keep in mind:

1. Movement happens at joints as one bone acts freely as the other remains relatively stationary.
   The bones can and do switch roles depending on the action you're making and the position you're in. An example is the comparison of hip flexion while walking versus while bending over. Both use the same hip action—flexion—but when you walk, your leg is freely mobile. When you bend over at the hips, your pelvis is the bone that is performing the movement.
2. Muscles are powerful, and their position optimizes their power. Muscles attach to bone on either end of a joint, crossing the joint space. In this way, muscles control the movement of the joint and also support the integrity of the joint space.
3. Muscle attachments are often named according to their functionality, so the label that's given to an insertion may include a reference to the bone that usually does the moving. For example, we walk more than we bend over at the hips. And the names of some of the muscles that go from pelvis to thigh bone reflect the fact that the thigh bone is the bone that moves while walking. The rectus femoris is a big bulky muscle at the front of your thigh. The word "femoris" refers to your thigh bone.
4. The part of the muscle located between two ends is known as the belly of the muscle.

The size, direction, and shape of a muscle and its attachments are part of what determines the range of motion and flexibility of the joint. These factors also help guide the best ways you can use to strengthen your different muscles.

Insertion of the Sternocleidomastoid Muscle or SCM

One prominent muscle in the neck is the sternocleidomastoid (SCM). The main job of the SCM is to turn and tilt your head, and it also assists when you bend your head forward or extend it backward. 

This muscle runs from the breastbone/collarbone (origin) to the mastoid process (insertion). The mastoid process is a little projection of bone located behind your ear. To feel the mastoid process, you can touch that tag of bone behind your ear with your finger.

The origin of the SCM actually divides into two parts, with each attaching to different, but nearby areas.

Each section of the origin is described as a head. One head of the SCM 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 starts mainly from the area around your hips and back and goes all the way to your upper extremity. This large muscle originates at the pelvis, ribs, thoracolumbar fascia, and some vertebrae.

Despite its size, the latissimus dorsi muscle eventually tapers to an insertion point that is located on the inside of your humerus. The humerus is the upper arm bone.