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H.hatze
06-23-1992, 10:50 PM
Dear Biomch-L readers,

Having read the Recommendations for Standardization in the Reporting of
Kinematic Data (Draft Version 4.1) and the respective and very thoughtful
responses of Jesus Dapena, Paolo de Leva, Herman Woltring, and Ton van den
Bogert, I would like to express my own opinion about this issue. My comments
will be very brief because of the extreme time pressure I am subjected to
at present.

Concerning PART 1: On this point I fully agree with the global coordinate
system as proposed by Jesus Dapena in his COMMENT A. An additional argument
for choosing this right-handed global reference frame (X toward the right,
Y forward, Z vertical) is the fact that it would be identical with the
one attached to the Kistler force plate and used extensivley throughout
the world. Finally, I would suggest using non-indexed capitals XYZ instead
of Xg Yg Zg or Xo Yo Zo, and that there should be only one global coordinate
system for 3D and 2D.

Concerning PART 2: Again, I fully agree with the COMMENT C aired by Jesus
Dapena. For most segments, the local coordinate axes would be approximately
parallel to the global one in the anatomical "reference pose". Also, a
number of human body models in use already employ this type of local segment
coordinate system.

The problem of using the same axes orientations for the segments on the
right and left side of the body and having to face changes in the signs of
some of the joint torque components for similarity rotations does not appear
to be a very serious one.

More disturbing is the fact that for some body segments (e.g., the abdomino-
pelvic segment) a principal axes transformation is required in order to
render the inertia tensor diagonal for purposes of dynamic modelling and
computer simulation. In practice, this implies a rotation of the segmental
coordinate systems passing through the segmental mass centers from their
"original" positions (however defined) to newly oriented positions.

There are, of course, many more important questions to be discussed as
H. Woltring has suggested in his comments dated 18 May 1992. These problems
need detailed and careful attention and should possibly be the topic of some
satellite meeting to an international congress on biomechanics.


Herbert Hatze
Vienna/Austria