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Kieran Moran
04-24-1996, 02:18 AM
Dear subscribers,

I have what may be a very simple question, but the answer to which is
very important to my studies. My PhD studies partly involve the
evaluation of Bi-lateral symmetry of the lower extremities during
vertical jumps. The results are being evaluated at the joint moment
level and, therefore, I require the determination of the point of
application of force.

I have access to two platforms which are located parallel to each
other ( and seperated by 5cm in the Z direction). With my subjects
facing in a positive X direction the point of application of force in
the X direction for each plate is equal to the moment of force about
the Z axis (Mz) divided by the total vertical force (Fy):

Ax = Mz / Fy (where moments are taken about the plate surface).

My results show a high degree of asymmetry, particularly during
depth jumps.

I now wish to DIRECTLY compare the results to a
commonly used method whereby the subject stands with both feet
on one platform and the kinematic data from one side of the body are
used. A DIRECT comparison is possible IF I can relate my
data from the two force plates to the condition "as if" only one
plate was used.

My question is:

>is Ax = the sum of moment of force about the Z axis for plates one
>and two devided by the sum of the vertical forces for plates one and
>two.
>
>is Ax = [ Mz(1) + Mz(2) ] / [ Fy(1) + Fy(2) ]

KIERAN MORAN

P.s.
(The coordinate system is the ISB system which is reactionary and
follows the left hand rule. Positive Y is vertically normal to the
force plate and positive X coincides with the direction the subjects
are facing)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% KIERAN MORAN
%
% EMAIL: KA.MORAN@ULST.AC.UK
% TELEPHONE: 0044 1232 368997
% FAX: 0044 1232 366863
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% BIOMECHANICS SECTION
% NORTHERN IRELAND BIOENGINEERING CENTRE
% UNIVERSITY OF ULSTER
% NEWTOWNABBEY
% BT37 OQB
% NORTHERN IRELAND
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