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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) ]

I appologise in advance if the answer is obvious.

Many thanks for your help

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
%
% BIOMECHANICS SECTION
% NORTHERN IRELAND BIOENGINEERING CENTRE
% UNIVERSITY OF ULSTER
% NEWTOWNABBEY
% BT37 OQB
% NORTHERN IRELAND
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