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one over there. They would think of them based on where they are located. In other words, as proximal and distal, or superior and inferior, etc. (Image 1) Why do I say this? Because when a muscle contracts, it doesn't treat one attachment any differently than the other. If we were to have a conversation with a muscle about its function, I imagine it would go as follows: Us: "Which attachment will move when you contract?" Muscle: "I don't know." Us: "Do you want one of the attachments and not the other to move when you contract?" Muscle: "No. I don't have a preference." Us: "OK. Well, which attachment should move when you contract?" Muscle: "Look, when I contract, I just pull in toward my center. I have no idea which attachment will or should move. If you want to know that, you need to talk to the nervous system." So why do we teach attachment terminology as origin/ insertion? I believe it is because of habit and momentum. It began this way many years ago, so we continue to do so. We learn it in school because our teacher learned it in school, and our teacher learned it in school because their teacher learned it in school, etc. (see Suzy sidebar). Why Origin/Insertion Terminology? So why might attachments have originally been described and taught as origin and insertion? Well, let's first define what an origin and insertion are. Most often, the origin is defined as the attachment that stays fixed when a muscle contracts, and is assigned to the proximal attachment. And the insertion is defined as the attachment that moves, and is assigned to the distal attachment. This is true in open- chain kinematics but is not true in closed-chain kinematics (see Open-Chain and Closed-Chain Kinematics sidebar). Open-chain kinematics are common in the upper extremity where the hand is usually free to move. But in the lower extremity, the foot is often in a closed-chain position against the ground, so closed-chain reverse actions often occur in the lower extremity. So perhaps the origin should be defined as the attachment that is usually fixed, and the insertion as the attachment that usually moves. And it is typically thought that the proximal attachment is usually fixed, and the distal attachment is usually mobile, so the proximal attachment is assigned the role of origin and the distal attachment is assigned the role of insertion. But if we are going to go that far, why not just describe the attachments as proximal and distal? It is far simpler. After all, origins and insertions can switch which one stays fixed and which one moves. But the proximal attachment is always the proximal attachment, and the distal attachment is always the distal attachment. Problems with Origin/Insertion Terminology The first problem with origin/insertion terminology is that it adds one more thing that the overwhelmed student must learn: the muscle's name, where the attachments are located, and what its actions are . . . and now, the student 38 m a s s a g e & b o d y wo r k m ay/ j u n e 2 0 2 3 Suzy I am reminded of the story of Suzy, a 5-year-old girl who sees her mother place a large ham for dinner onto a cutting board and cut off three inches from each end before placing it in a tray and putting it in the oven. She asks her mother why she does this and her mother replies that her mother taught her to do this. So, they drive down the street to where Suzy's grandmother lives and they ask her why she taught Suzy's mom to do this, and she replies because her mother taught her to do it this way. So, they go downstairs to where Suzy's great-grandmother lives, and they ask her why she taught Suzy's grandmother to do this. She replies: "Well, when I was young, the oven wasn't large enough to fi t the ham, so we had to cut off some from each end." The point here is that there might have once been a good reason to do or learn something a certain way, but that reason might no longer exist; yet we continue to teach and learn this way just because we have always taught and learned this way. The proximal and distal attachments of a muscle. Images permission by Dr. Joe Muscolino, Kinesiology, the Skeletal System and Muscle Function, 4th Edition, 2023, Elsevier. 1 Distal Proximal