Muscle Insertion and Your Joints

The insertion of the muscle is defined as that end of the muscle that attaches 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, where 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, but such is knowledge is a bit more advanced. (The Pilates method takes advantage of this phenomenon in the design of exercises that work your "anti-gravity" muscles.)
      That said, a brief example is the comparison between walking and bending over while in a standing position. 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.
    • Muscle attachments are named with this in functionality mind, so the label is given to an insertion (one of the two types of attachments) generally includes a reference to the bone that does the moving most of the time. In our walking versus bending at the hip example above, we walk way more than we bend over at the hips. This means that some of the muscles that go from pelvis to thigh bone reflect the fact that the thigh bone is freely movable during walking. An example of this is the rectus femoris, that big bulky muscle that lives at the front of your thigh. The word "femoris" refers to your thigh bone.
  • Muscles are powerful engines for movement. This is by design; they attach to bone on either end(s) of a joint, crossing the joint space as they do. In this way, muscles control the movement of the joint and also support the integrity of the joint space. (As you probably know by now, attachment points are either the muscle origin or as we're discussing in this article, the muscle insertion.) 
  • 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. These also help determine the way to get your muscles strong.

woman holding her shoulder.
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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 (from the mastoid process, which is a little projection of bone located behind your ear at the bottom) to your breastbone and collarbone.

The main job of the SCM is to turn and tilt your head, but it also acts as an assistant when you either bend your head forward or extend it backward. (By the way, to feel the insertion of the SCM, the mastoid process, you can touch that tag of bone behind your ear with your finger. This may give you a greater sense of what we're talking about here.)

As we alluded to just above, the origin of the SCM, i.e., the normally stable end of this muscle, and the end that is opposite to the insertion, actually divides into two parts, with each attaching on different, but nearby areas.

We can now unpack this a bit more: The parts are called "heads." One head of the SCM 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 starts 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 an insertion point that is located on the inside of your humerus. (The humerus is the name given to the upper arm bone.)

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  • 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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