PDA

View Full Version : Summary for Body Center of Mass



Sergio Fonseca
10-07-1996, 02:29 AM
I want to thank all of you that answered my question. Below follows my
original question and a summary of responses I received.

Sergio Fonseca (fonserte@bu.edu)
Dept. of Physical Therapy
Boston University


Original Posting:
----------------------------------------------------------------------------
--------------
I am a physical therapist and a doctoral candidate doing my research work
in locomotion in children with cerebral palsy. I would like to know about
the availability of a software for 3D calculation of body center of mass
during walking that does not assume side symmetry. We are using a two
position sensor Optotrak system to generate 3D kinematic data from both
sides. Program codes (basic or C) in which the anthropometric variables can
be changed to accommodate different age groups (ex: Dampster or Jensen) are
preferable.



Replies:
----------------------------------------------------------------------------
-------------------------
Sergio,

I am working on a project for the Air Force to validate some software
which calculates the whole body center of mass and moments of
inertia. It allows the user to input anthropometric data and also
has an option for children where all that you input is age, weight,
and stature. There is one piece of software called GEBOD (GEnerator
of BODy data) which generates segment information and another called
ATB (Articulated Total Body model). And, the other piece of good
news is that this software is in the public domain. I don't really
know of any other software that determines all of this information in
3D.

BUT, one of the problems that we're finding with the software is that
it assumes symmetry. However, as I write this, I'm thinking that
GEBOD could be run twice--once for each side of the body, and you
would have to use individual anthropometric measurements for this to
work--then ATB could be modified so that it could take input from
both sides of the body to calculate 3D CG or center of mass. The
code is written in FORTRAN, but the listing would be available to
you.

If no one else suggests software that does not have a symmetry
assumption, I would say that this would be painful and tedious but
doable.

Beth Todd

Dr. Beth A. Todd
Assistant Professor
Mechanical Engineering
Box 870276
University of Alabama
Tuscaloosa, AL 35487-0276
btodd@coe.eng.ua.edu
(205)348-1623
fax: (205)348-7240

----------------------------------------------------------------------------
---------------------------
From: Gideon Ariel

Check the web site at: http://www.arielnet.com

----------------------------------------------------------------------------
--------------------------

I had some thoughts on your problem, which you posted on BiomechL. If you
use the method of Yeadon and Morlock for estimating limb segment inertial
properties, (J Biomech, vol 22, p 683-9, 1989) and also the method of
Dempster for estimating CoM of each limb, given by Winter, in
Biomechanics and Motor Control of Human Movement 1990, it is possible to
easily derive a kinetic model which is not dependent upon symmetry
assumptions, however you need to make anthroprometric measurements on each
subject. If you are interested I have some Matlab code for implementing
the method of Yeadon and Morlock, but this problem is fairly simple. The
real problem lies in a good algorithms to determine key positions of
joint centres which allow for pathology, age, sex, deformity, etc. It
really depends upon which part of the gait cycle you are interested in;
if it is the stance phase then the joint centre positions are of great
interest, else for swing the movement of CoM and the limb inertial
properties are of greater interest. Although some work has been done to
determine estimates of the instant joint centres of normal joints I know
of little work that has attempted to determine the same thing for
pathologic joints, perhaps for good reason. It is difficult to establish
an absolute pattern of movement for a so-called "normal" joint. The
problem becomes so much more intractable for any joint displaying a
degree of pathology or deformity.

Richie (H.S.) Gill
Oxford Orthopaedic Engineering Centre
University of Oxford
Nuffield Orthopaedic Centre
Headington
Oxford
OX3 7LD

email: richie.gill@ox.ac.uk
tel : +44 1865 227541
fax : +44 1865 742348

----------------------------------------------------------------------------
----------------------------
Hello Sergio,

Sorry, but I can not help you in the way you want, but I am sure
that it is not difficult to write a program to calculate it.

In engineering terms, it is a simple task to calculate the CM if
you have the spatial position of the limbs.

Anyway, I am PhD student also.


Carlo Pece Phone: +44 (0)1784 431341 ext:244
PhD Researcher Fax: +44 (0)1784 472879
Brunel University
Department of Design E-mail: Carlo.Pece@brunel.ac.uk
Egham
Surrey TW20 0JZ
UK

----------------------------------------------------------------------------
----------------------------

Hi there!
U may want to get in touch with Prof. C.L Vaughan at the University of Cape
Town. His Email Address is KVAUGHAN@ANAT.UCT.AC.ZA
hope this helps,
Cheers,
Noddy


\@/
@@@ \\|//
@@@@@ \\\|///
( @ @ ) ( O O )
____oOOo______^_____oOOo_____oOOo______O______oOOo ____
| |
| Nivedita Subramanian |
| Sackler Institute of N |
| Biomedical Sciences O |
| 550, 1st Ave, New York, D |
| NY 10016, USA D |
| Tel. +91 (212) 696 4693 Y |
| SUBRAN01@popmail.med.nyu.edu |
|_________________________________________________ ____|