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Measurement of human arm's position and torque

KP_PC k.p.collins at worldnet.att.net
Thu Nov 6 15:50:46 EST 2003

"Panagiotis Artemiadis" <partem at mail.ntua.gr> wrote in message
news:bocp31$28io$1 at ulysses.noc.ntua.gr...
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| But what about the mass of the human arm?

In vectorizing the body's motion, the mass of the
body [the arm] can be treated as constant. Con-
stants drop out of the calculations. [In reality,
there are moment-of-inertia changes as muscles
contract and expand, and as generalized con-
sequences of exercise [fluid loss and its dist-
ribution, stored-energy consumption, oxygen
intake, vasodilation, etc.] but if you want to
calculate at that 'level', you still have to construct
a 'platform' for calculating at that 'level' by, first,
doing the simple thing.

I gave you all you need in my prior post - except
that you need at least two cameras if you don't
want to 'guess' with respect to 'depth' info in a
single camera's field of view. Orient the cameras'
viewing axes at right angles [cheap internet cam-
eras will do.

All the calculations you need can be found in an
introductory Physics textbook. Thumb through
the first few chapters looking for lever-arm prob-
lems. The body's skeleton is just a bunch of
such lever arms.

Come to think of it, there should be software
that help you with all of this - look up Fractal
Design Poser. I don't think it does stuff with
added masses, though, but perhaps it would
help provide the vectorization as data that you
could use.

It's an interesting exploration with respect to
nervous system function. I can't toss anything
at a waste basket, or a garbage bin, without
marvelling at the great ease with which nervous
systems calculate the necessary effector act-
ivations, despite the widely-varying masses
that can be involved [including the inferior
olive's 'crumpled-bag' nucleus coordinate
system translation dynamics that are dis-
cussed, and reduced to TD E/I-minimization,
in AoK, Ap6 [for those who have AoK].

But, sorry, I won't do the calcs for you.


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