It is very interesting to read the discussion on the ISB kinematics
convention in the list.

Although I agree that this ISB standardized kinematics convention should
follow the international standards and commonly accepted practices in
physics and mechanics, I don't think how to labelling axes is a very
important issue in this business. The purpose of standardizing
kinematics convention should be well justified first.

Why should the convention be standardized? For the convenience of
sharing data? I don't think this is a good argument for this
standardization. It should not be a problem to transfer data from one
coordinate system to another as long as the definitions of both system
are clearly described. Besides, how many biomechanics research groups
are sharing data? If it is not a common practice, why should all people
in biomechanics use the same system for the convenience of a small group
of people?

It may be a good argument that this standardization will make the
description of the coordinate system easier in publicatins and
thus help to shorten the lengths of those papers for journals. If this
is the main purpose of this standardization, more than one definition
should be recommended for the convenience of majority, if not all, in
biomechanics research community. In the technical note by Wu and
Cavanaph, only one rotation order was recommended without any
justification for the use of this rotation order. This really concerned
me. It is known that there are many different rotation orders and the
results of rotation could be quite different for different rotation
orders. A given order of rotation may have some advantages for some
joints in some research work but may not for the other. I do think that
the order of rotation should not be standardized or multiple standards
should be recommended.

This standardization may be more complicated than it was thought. ISB
may need further considerations before any recommendations are made.

Bing Yu, Ph.D.
Orthopedic Biomechanics Laboratory
Mayo Clinic
Rochester, MN 55905