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I grew up with orthopedic surgeons as my parents. My toys as kids were these little models of kne​e / shoulder joints that I could play with - you could break off the cartilage and show all the individual tendons. Then, I went off to college and there was a stint of time where I was biomedical engineering, so I have a pretty good knowledge of the human body. 

Controls came into my life and I realized that the human brain in really just like a central computing unit, and the rest of the body is operating off of information/neurons firing from there. Not an original thought.

 

Then, I started to think a bit about how a finger actually moves. Is there a delay? Is there more precise movements in each of our fingers?

 

Why is the just noticable difference in the shoulder joint smaller than at the finger or wrist? Is it due to the distance away from the center computer (brain) or due to joint mechanism itself or perhaps the mechanical mass/ intertia of each joint. 

I went searching for answers - I did find any. I didn't really even find any that cared enough about these tiny differences to speak on them. But, I am hypothesizing it is a combination of all three of those factors + more... but how does our body so seamlessly account for these joint changes? I want to understand that a whole lot more, but this made me realize I could never do the controls on a robotic arm! 

Next ... 

Got pretty deep down this path and found that there is more intermittency (or radical changes) in movement on the distal side of the arm rather than the radial. 

There's some hypotheses as to why, but the one I thought was the coolest was this: our arm acts as a low pass filter for "noise" coming from our joints and the proximal points have a lower cut-off frequency than our radial parts. This noise does not effect the kinematics and dynamics of the joint path of motion, but it does change the movement intermittency. 


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