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Summary for Body Center of Mass

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  • Summary for Body Center of Mass

    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:
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    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


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