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Neil Mansfield
01-22-2003, 06:43 PM
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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