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  • Summary of responses to field testing markers

    Hi,
    Here is a summary of the responses I received in reply to the
    request below. Thanks to everyone who sent a reply the suggestions have been
    great!

    You may want to experiment w/ elastic bands. If your marking joints, bands
    may be used depending on the excursion of the joints during the activity.
    The greater the excursion the higher the likelihood that the marker is
    displaced. If the joint does move into extreme flexion (ie.
    knee and elbow) you may want to try partially splitting the band. The split
    band should allow for the bony apex of the joint (ie. patella and olecranon)
    to penetrate the band.

    I have seen this method used w/ controlled lifting tasks. Not the best, but
    a possible solution.

    Ray McKenna


    your problem could be solved if you make a pilot study first where you try
    to avoid any markers and digitize with a good understanding of the location
    of the anatomical landmarks. Let several colleagues (n>10)digitize identical
    trials several times. Then test the results concerning inter- and
    intraindividual variability and reliability of results. You might come to
    the conclusion that the error is small enough
    so you can do the work without marker-bound digitising. In sports events we
    have similar problems although the athletes do not wear sloppy uniforms.

    Yours

    Axel


    ask them to wear elastic bands or knee guards over their pants. the markers
    can be attached on these.
    but be warned that it can get quite uncomfortable for the guys over the long
    distance. Abrasion of the pants on the skin, blood flow problem (if elastic
    band is too tight), heat accumulation inside the pants etc.

    Tan Juay Seng

    I'm an undergraduate biomedical/biomechanics senior at Case Western Reserve
    in Cleveland, and I haven't actually done any research, so take this
    suggestion for what it's worth.
    Why couldn't you just use some type of elastic bands that had your markers
    permanently attached to them. Then you could stretch them on the legs of
    the soldiers right over the uniform. If they were tight enough, they
    wouldn't move or fall off, creating the fixed point you need. They would
    also be removable (your sensors would not be permanently attached to the
    uniform, just the band) and slightly adjustable. You might need to be
    concerned with restricting motion, but if they are small, it probably
    wouldn't matter much.

    Good luck with your project,
    Erin


    This is a fundamental problem! It's impossible to measure motion through
    shirts and pants. No chance.
    But there are some tricks to try an approximative recognition of
    motion:
    1. Strap your markers with elastic tape onto the leg and arms.
    2. Glue the clothes on the skin ( use some glue, which can be washed
    out, e.g. paste for wallpapers or wheat glue) and stick the markers on the
    cloth.
    3. Let the subjects take thier clothes off -- the only scientific
    way.
    4. Buy new clothes after cutting holes in the original ones --
    motion analysis isn't cheap, nobody could expect that.

    Wishing you had further ideas, our lab and all other labs I know
    don't believe in measuring through clothes.

    Best regards, Jan Simon
    GaitLab, Orthopedic Dept. of the University Heidelberg
    IWR, Interdisciplinary Center for Scientific Computing, Heidelberg


    The fact you need specific landmarks for your "biomechanical
    analysis" would suggest that you have a set of derived variables you wish to
    consider. i.e angle of knee flexion and hip extension. This is not very
    accurate with baggy clothing. Magnetic markers are unlikely to stay on for
    such a duration and you will have a very small sample size. You may wish to
    consider these for a validity study to see if assessing surface estimates
    from video are associated with the magnetic data outputs.

    Therefore you may wish to look at more global markers of fatigue/capacity by
    assessing more subjects (i.e all of the recruits) by recording standard gait
    parameters such as cadence, stride length etc. (get them to run through a
    single file gate every 3 km - better if you could get some ID therefore a
    within subjects design would have great statistical power). With this data
    you can have a general
    idea of the changes over time. Since the normal variations of individuals is
    likely to be large an analysis that looks at changes over time may be of
    more interest. You may wish to mark the COM of the back pack and see where
    it sits relative to other landmarks, i.e the tragus, the shoulder hip the
    horizontal / vertical distance from heel strike, etc. of course getting them
    to run over (jump down onto
    would be better for motor control reasons) a set of force plates to look at
    the changes in the rate of loading (impact) would be very interesting but
    alas that could be difficult to organise in a field test!

    Good luck.
    Garry Allison.


    How about sowing the markers onto loops of elastic bands, these
    appropriately sized bands can then be slipped over the limbs to the required
    position.

    Gary Dennis
    School of Physiotherapy & Exercise Science
    Griffith University (Gold Coast)
    ph +61 07 5552 8357
    G.Dennis@mailbox.gu.edu.au


    Try to soak up the uniform with glue in places where you plan to attach
    markers. Then glue the uniform to the subject's skin and the markers to the
    uniform. This method worked well with skaters, but their suits were much
    thinner and easier to wash afterwards.

    Boris Prilutsky

    ..don't know what type of marker/spatial model setup you are using or what
    kind of equipment your are using to digitize, however, I digitize athletes
    performing in their own environment (games, practices, training, etc.) for
    biomechanical performance/injury evaluation and the only way I have found to
    successfully get around the issue of markers and altering the activity is to
    manually digitize. If done properly, you will avoid marker movement, hidden
    points, the issues of marker attachment and the risk of altering the
    activity.

    Chris Welch


    Three potential thoughts, and I am sure someone has already
    suggested the first: 1) Double sided carpet tape: only
    problem is that it may not be strong enough for the entire
    15km march. Plus problem with the free swinging marker is
    not really solved. (2) Velcro: Possibly sewn on temporarily?
    Most stiches leave minimal marks on the material. Again
    problem with free swinging markers, unless some way of
    stopping the pants material from moving is used. (3) Use
    elastic cuffs: Have seen these where the marker is set on an
    elasticised cuff that may be slipped over the limb, and over
    the clothes. (Sort of like a big rubber band.)

    Hope this helps.

    Good luck!

    Daniel Magnusson

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