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

%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

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

%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%