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  • Re: whole-body vibration

    Arno,

    It is very difficult to calculate vertebral vibration from skin mounted
    markers or transducers. There are two problems: skin movement and vertebral
    rotation. You can use an impulse response method to calculate the local
    skin movement and to then create a correction transfer function to apply in
    the time domain using convolution. This is described in Kitazaki and
    Griffin, 1995 (J.Biomechanics). This works best for continuous vibration
    with a low crest factor; I would be concerned to use it with impulses. (The
    only data I know of that used impulses also used K-wires).

    Vertebral rotation is very tough to compensate for without invasive methods.

    I have also published on this topic: the most relevant are
    Mansfield NJ and Griffin MJ (2002) Effects of posture and vibration
    magnitude on apparent mass and pelvis rotation during exposure to whole-body
    vertical vibration. Journal of Sound and Vibration 253(1) 93-107.

    Mansfield NJ, Holmlund P, Lundström R (2001) Apparent mass and absorbed
    power during exposure to whole-body vibration and repeated shocks. Journal
    of Sound and Vibration 248(3) 427-440.

    and

    Mansfield NJ and Griffin MJ (2000) Non-linearities in apparent mass and
    transmissibility during exposure to whole-body vibration. Journal of
    Biomechanics 33(8), 933-941.

    I would be very interested to hear how you get on - if it works, then new
    possibilities would open up. Keep me informed!

    I wish you success,

    Neil.

    ____________________________
    Dr Neil J Mansfield
    Department of Human Sciences
    Loughborough University
    Loughborough LE11 3TU, U.K.
    tel: +44 (0)1509 228483
    fax: +44 (0)1509 223940
    http://humsci.lboro.ac.uk/vibration

    ----- Original Message -----
    From: "Arno Grunendahl"
    Sent: Wednesday, January 22, 2003 3:19 PM
    Subject: whole-body vibration


    > Dear colleagues,
    >
    > today we measured the relative displacement of marker points, placed
    > along the spine, during jumping with a VICON-system.
    > The question is how can we calculate the relative displacement of single
    > vertebrae from the collected data, as it contains the displacement of
    > skin etc.
    > The global aim is to measure whole-body vibration, i.e. accelleration
    > and displacement would be relatively low.
    >
    > Maybe somebody has dealt with the same problem and will share his/her
    > experience.
    >
    > Thanks in advance,
    >
    > A. Grunendahl
    > --
    > The king said sail, but the wind said no.
    >

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