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dhahn90
02-28-2007, 11:38 PM
Dear community,

My field of interest are force-length-velocity properties of
multiarticular leg extension movements. Based on experimental data
(external forces, kinematics), I am doing an invers-dynamic modelling
approach by using VICON BodyBuilder Software. To account for inertial
properties of the lower extremity segments, there is a anthropometric
model implemented in the software that is based on the data of Dempster
(1955). For modelling, the software needs three input-parameters for
each segment:

1. segment mass relative to total body mass (m)
2. centre of mass position relative to segment length from the distal
endpoint
3. radius of gyration relative to segment length for the cenre of mass
(p)

The relevant values for these parameters are taken from Winter, D.
(1990) Biomechanics and motor control of human movement, pp 56-57.

Now, my problem arises from the fact, that I would like to use
alternative anthropometric data from the model of Zatsiorsky (1983,
2002). In doing so, the first to parameters can be taken from the work
of DeLeva (1996) who adjusted the Zatsiorsky model to commonly used
segment definitions.
However, unfortunately DeLeva do not present corresponding values for
the radius of gyration for the centre of mass and I don't get the clue
how to determine this parameter correctly. In general, the moment of
inertia about the centre of mass is given by

I = mp^2

Thus I am looking for p, which is given by

p^2 = I/m

whereby, according to the parallel axis theorem, I can be calculated by

I = Iprox. - mx^2 (Iprox. = moment of inertia about the proximal end of
the segment; x = distance of the centre of mass from the proximal end)

When using the data of Winter (1990) there is no problem in calculating
Iprox., as there is only one value given for the radius of gyration
about the proximal end (see table on pp. 56/57 in Winter 1990). In
contrast, DeLeva presents 3 radii of gyration, one for each segment axis
(p. 1228 in his paper), and thus I do not know which one to take for the
calculation of Iprox.

So, if anyone knowes how to determine Iprox. correctly, it would be of
great help!

Thanks for all replies,
Daniel

de Leva, P. (1996a). Adjustments to Zatsiorsky-Seluyanov's segment
inertia parameters. J Biomech 29(9), S. 1223-1230.
de Leva, P. (1996b). Joint center longitudinal positions computed from a
selected subset of Chandler's data. J Biomech 29(9), S. 1231-1233.
Winter, D. A. (1990). Biomechanics and motor control of human movement.
New York, Chichester, Brisbane, Toronto, Signapure: John Wiley & Sons.
Zatsiorsky, V. M. (2002). Kinetics of Human Motion. Champaign, IL.:
Human Kinetics.
Zatsiorsky, V. M., Aruin, A. S., et al. (1984). Biomechanik des
menschlilchen Bewegungsapparates. Berlin: Sportverlag.

__________________________________

Daniel Hahn (PhD Student)
Department of Biomechanics in Sport

Technical University of Munich
Faculty of Sport Science
Connollystr. 32
D-80809 Munich

Tel.: +49 89289-24583 Fax: -24582
Email: d.hahn@sport.tu-muenchen.de