PDA

View Full Version : ADDENDUM:analyzing force platform kinetics



Young Hui Chang
07-25-1995, 03:48 AM
There seems to be a slight need for clarification on my previous posting;
mostly on the effect of a pure torque on the movement of an animal's center
of mass (thanks to Paulo de Leva for pointing it out!).

(By the way, for the record, I am still a grad. student so please don't
give me my degrees too easily when responding).

-----
My original posting asked for (1) approximate levels of moments PRODUCED ON
THE GROUND BY THE FOOT in the vertical axis. I would only like this
information in order to have something by which to compare my own data.

However, I am doing kinetics of a different sort than is conventionally
done. My 6 degree-of-freedom transducer was mounted ABOVE the animal (on
the "ceiling) and was used to measure animals that arm-swung beneath it
(grabbing on to it at a defined handhold).

Thus, relative to my second question, the animal is able to grab on to its
superstrate (something not commonly seen in terrestrial locomotion). True,
a pure moment about the cranio-caudal (or vertical axis) shouldn't alter
the translational path of the center of mass. However, the issue of moments
applied about the horizontal plane of the transducer is very real in
brachiation (arm-swinging locomotion) whereas this is not the case in
terrestrial locomotion.

So my 2nd question is about (2) the EFFECT OF PURE MOMENTS (produced by a
hand gripping onto an overhead "branch") UPON THE MOVEMENT OF THE ANIMAL'S
CENTER OF MASS which is presumably some distance beneath the application of
the torques.
-----

My original posting follows below (my apologies for using so much of your
disk space):
--------------------------------------------------------------------------------

Hi all,

I've got a couple of questions for those who have had experience dealing
with force plate data. It seems in all of the literature I've been able to
find on force plate data that moments at the foot-ground contact are
neglected (I've been told that this is because the moments applied to the
ground are insignificant). I have not been able to find any literature that
documents what magnitudes of torque are considered "insignificant." (note:
I have seen much data on JOINT moments, but none on foot-ground contact
moments).

-----
1) Does anyone out there know what moments are applied (rough estimate is
fine) by the foot (human or other terrestrial animal) during a walk or
run/trot? (or of what ref's to check?)

(I am analyzing some data on brachiation kinetics (of arm-swinging
hominoids) and it seems that the moments may be "significant.")

-----
We often use integration of the animal's accelerations (from force data) to
get velocity and position data. However, this is (again) neglecting torques
produced by the animal.

2) If the moments applied at the limb-surface contact are substantial, how
does that affect the velocity and position of the center of mass? i.e.,
what is the integral of a moment? (a tangential velocity?)

Thanks in advance to those replying. I will post all replies unless asked
otherwise.

Young Hui

------------------------------------------------------------------------------
Young Hui Chang
Department of Anatomy phone: 607-253-3551
College of Veterinary Medicine fax: 607-253-3541
Ithaca, NY 14853-6401 e-mail: (yhc3@cornell.edu)

"If you can't hear me, it's because I'm in parentheses." -Steven Wright
------------------------------------------------------------------------------