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Prof. Hatze
09-26-2001, 06:06 PM
Dear Dr. Panero,

I am responding to your question via BIOMECH-L because your problem may
be of general interest.

The approximation of body segments by rigid bodies is not only
inadequate for situations in which impact loads are imparted on the body
but, in principle, for all situations in which substantial local
accelerations occur at body segments. This is one of the major problems
in forward dynamics (motion simulation) and also in inverse dynamics
(motion analysis). I am analysing these questions in a forthcoming paper
in the Journal of Biomechanics (H. Hatze: "The fundamental problem of
myoskeletal inverse dynamics and its implications", to appear soon).

The truth is that apart from the bony parts of the skeleton, there exist
no real segments in the body. In fact, it frequently happens that large
soft tissue components span the joints, as is the case in the hip and
shoulder regions.

The conclusions to be drawn from this is that we require totally new
models of the human body in which rigid elements are combined with
elastic ones. My group is working on this problem but it turns out to be
awfully difficult requiring treatment involving partial differential
equations.

However, in my opinion this is the only way to eliminate the discrepancy
between model predictions and dynamic observables such as ground
reaction forces.


Herbert Hatze




************************************************** ******
Prof. Dr. Herbert Hatze
Head, Department and Laboratory of Biomechanics, ISW,
University of Vienna

Auf der Schmelz 6 Tel: + 43 1 4277 48880
A-1150 WIEN Fax: + 43 1 4277 48889
AUSTRIA e-mail: herbert.hatze@univie.ac.at
************************************************** ******

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