Muscle origin is a term referring to one end of a muscle, generally at the location where it attaches to a bone. The main part of the muscle called the belly of the muscle, then crosses over the gap between this bone and another usually adjacent bone — to attach there. The end of the muscle that attaches to the second bone is called the insertion.
Muscle origins and insertions are also called muscle attachments. When you phrase it this way, you are not distinguishing the type of attachment. In other words, an attachment can be either an origin or an insertion, or with a plural usage, both.
Muscle origins are distinguished from muscle insertions by the relative degree of movement (and therefore the role of movement) of the bone to which they attach when you perform common motions.
Muscle origins generally attach to bones that provide stability.
Origin and Insertion Role Reversal
That said, it’s possible to reverse the roles of the bones (and their muscles) that are involved in a common movement so that the usually mobile part provides the stability and the usually stable part does the action. In this case, though, the motion will be very different than the original version. Not only that, the resulting action serves an entirely different purpose.
This kind of reversal can be valuable as you do strengthening and/or flexibility exercises. By working the joint from the opposite-from-usual perspective, you may find new muscle fibers to work and train them to function for you in more than one situation. Plus, you'll likely increase strength through a larger range of motion — a great way to decrease your risk of injury. Pilates machine workouts are known for this type of training. If Pilates is too expensive for you, consider using a theraband and/or tubing.
With most of the band exercises, you'll get a chance to work all the muscles around a joint using at least 2 types of contractions. The key to a great workout here is to keep a slow speed both there and back without sacrificing good form.
Muscle Attachment Knowledge for School
When you study muscles and joints for school, you’ll need to learn the exact locations of the muscle origins and insertions — along with other information such as the action they produce for the joint. You may also need to know the nerves that supply the muscle. Keep in mind that muscle origins and insertions sometimes attach on several places on their respective bones, and your teacher will probably require you to know all of them.
To recap, and propel your studies forward, here are 4 handy points for understanding the role muscle origins and insertions play in human motion:
Muscles are powerful engines for movement; they attach to bone on either end, crossing the joint as they do.
The part of the muscle located between 2 ends is known as the belly of the muscle.
Movement happens at joints, with one bone of the joint moving freely as the other remains stationary.
All of this is significant because of the size, direction, and shape of the muscle belly and muscle attachments are part of what determines the range of motion of the joint, and therefore its flexibility.