In human balance, how do CoP and CoM relate to each other? A small thing, but it is amazing how often people get this wrong. CoP (relative to ankle joints) is a measure of torque, while CoM is a measure of body movement. #balance #posture 🧪 - ThreadSky

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cybal.bsky.social • 87 days ago

In human balance, how do CoP and CoM relate to each other? A small thing, but it is amazing how often people get this wrong.
CoP (relative to ankle joints) is a measure of torque, while CoM is a measure of body movement.
#balance #posture 🧪

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cybal.bsky.social•87 days ago

CoP fluctuates around the CoM projection, thus they do behave similarly at low frequencies (<1 Hz). But I think it is wrong to call it 'sway' as most people do.

Is this just nitpicking on my side?

popkirov.bsky.social•86 days ago

Can you elaborate why it's not sway?

cybal.bsky.social•86 days ago

Sure, sway is a kinematic variable: Body movement. CoP is the center of pressure or force and therefore a dynamic variable. In class I ask students to feel the the CoP, stand in neutral position and the push back or to the side. You will feel the CoP initially go the opposite direction of the CoM.

popkirov.bsky.social•86 days ago

That makes sense, thanks!

jvandieen.bsky.social•87 days ago

I don’t think is is nitpicking. I have seen reviewers and authors suggest that balance control is about COP and even question why one would look at COM. Imo it is about control of the COM relative to the base of support. The COP is an easily measurable byproduct of how the COM is controlled.

cybal.bsky.social•87 days ago

Why byproduct. Isn’t CoP distance to joints proportional to the generated torque? I.e. the muscle output of the control mechanism. But I think looking at CoM is valid too, as it’s a closed loop system… I mostly use CoM.

jvandieen.bsky.social•86 days ago

It is not a direct reflection of ankle moments albeit a reasonable approximation. But what I meant is that the CoP is not of interest in itself. The ankle moments are but even then they are the means to an end (controlling the CoM)

cybal.bsky.social•86 days ago

Fair points 😁

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