There’s more to your flexibility than muscles.
Your bones play a big role in your range of motion.
Joint surfaces are the parts of bones that touch other bones and permit sliding, spinning and rolling of your bones across one another.
This permits your bones to move and your body parts to travel through space. Variations in bone morphology (bone shape) influence how your joint surfaces slide, spin, and roll across each other. This, in turn, influences how much you can move at your joints, which will play a role in how flexible you are within particular body positions.
This video provides a quick visual of a pretty common variation in people’s thigh bones called femoral retroversion. It’s basically a torsion (or twisting) of the shaft of the femur. This variation is not a pathology or even a problem. It’s different bone structure, similar to how the bone structure of our individual faces are all shaped differently, which is one of the main ways we are able to recognize each other as individuals. Facial recognition software is designed specifically to notice things like structural variation of our facial bones.
While there’s no such thing as thigh bone recognition software, our individual femur bones are shaped uniquely, as well. Just like the bones of our faces!
For movement teachers, structural variation is great to know about, especially for the bones of the major joints of our body, like our hip joints. This awareness can play a part in helping us understand why, for some people, certain positions, movements, or stretches come easier, while for others they are harder.
For example, people with femoral retroversion might be able to do lotus pose much more easily than people who don’t have this particular morphology of their femur bones. Additionally, people with femoral retroversion will likely have to squat differently than people who don’t have this particular morphology.
But actually, my favorite reason to have a basic understanding of common bone morphologies is to know that, when it comes to this type of anatomical variation, there’s a lot that we just can’t know as movement teachers. It’s outside of our scope of practice to assess these variations in our students, whether manually or through movement assessment. It’s also outside of our scope of practice to diagnose students with these morphological variations.
What it boils down to is…bone broth.
What it boils down to is recognizing the liklihood of variation for all of the major joints of the body in all of our students.
This can help us remember that we don’t always know what could be causing a students limited range of motion. It can open our mind to consider that if someone is not able to do a pose because of limited range of motion, it might be related to more than just soft tissue flexibility (think fascia, ligaments, and tendons), or muscle function.
Sometimes there’s a very hard, bony truth to range of motion limitations. We won’t change this with more stretching or strengthening.
Ultimately reckoning with and acknowledging this unknown is good teaching ethics. It’s good epistemological hygiene.
Epistemology is the study of knowledge. It looks at how we know what we know. It pays close attention to the limits on what we can know. Movement teachers don’t have MRI technology, for example.
This awareness of the limits of what we can know as movement teachers might prevent us from going beyond our scope of practice and making false assumptions about our students. It can also help us maintain curiosity for the differences we see amongst our students. This can make us better observers.
In both cases, when we are better observers and we stay within scope of practice, we avoid harm.
We may also be more effective at helping our students feel better and move better, too.