H. HATZE ON 28 SEPT. 1995

Instead of presenting a summary listing of all BIOMCH-L contributions

to the above topic, I shall attempt to give an objective resume.

A total of 19 contributions was received which includes those
directed to my personal e-mail address. Of these 19 contributions, 15

(or 79%) expressed outright rejection of the proposed ISB recommend-
ations, in some cases rather emphatically ("We have no intention of
ever using the proposed (ISB) conventions"). Of the remaining 4
contributions only one (that of Dr. Jack Crosbie of the University of

Sydney) expressly supported the ISB standard, while in 3
communications (those of Barbara van Geems, South Africa, Hamid
Rassoulian, Dr. J. H. Lawrence III, University of Kentucky) arguments

were presented that could possibly be classified as partial support
for some aspects of the ISB recommendations.

I shall now briefly react to the arguments put forth in the 4
communications that could be seen as support for the proposed ISB

Dr. Crosbie's argument rests on the 2D-presentation of motions in
the plane of progression which, in his opinion, should be the
XY-plane. A similar argument is also used by Wu and Cavanagh on page
1258 of their J. of Biomechanics paper with the addition that such a
presentation "... will be consistent with the three-dimensional
convention." If the internationally adopted 3D-convention for
Cartesian axes systems is meant then this statement is not true as I
have shown by means of many examples from the international
literature. In addition, and in complete agreement with the opinion
expressed by Dr. Scott Tashman of Case Western Reserve University
("3D analysis is a completely different world than 2D analysis" and
"... basing a 3D standard on 2D conventions makes little sense"), 3D
analysis and simulation are the dominating techniques in todays
biomechanical research which fact should be used as point of
departure for any standardization attempt. Also, in any
two-dimensional (sideward) motion in the CORONAL PLANE, the YZ-plane
(in the ISB convention) would be the plane of progression and
therefore the XY-plane argument completely breaks down, although such

a motion analysis would certainly qualify as a ligitimate 2D-motion
analysis, albeit in the coronal plane. The remarks just made also
to the opinion expressed by Hamid Rassoulian ("the plane of
should always be labelled XY").

The arguments advanced by Barbara van Geems of the University of Cape

Town and based on photogrammetric considerations are also not
convincing. Again, she assumes the recording of a 2D motion executed
in the sagittal plane only, in which case the photographic XY-plane
would coincide with the spatial ISB standard XY-plane. However, in
3D-recording more than one camera are used of which most will be
situated in oblique positions relative to the spatial coordinate
system and certainly not such that the spatial Z-axis always
coincides with the optical axis of the camera concerned. Quite to the

contrary, the optical (z-)axis of a head-mounted camera would be in
line with the ISB-standard-proposed Y-axis.

Finally, the opinion expressed by Dr. J. H. Lawrence III of the
University of Kentucky also (implicitly) assumes ONE plane of
activity ("I believe that the key to maintaining convention when
setting up a 3-D orthogonal measurement system is to establish
Cartesian coordinates in the plane of the activity"). It must be
reiterated that, by definition, 3D-motion analysis and simulation is
not restricted to one plane of activity and, in general, not even to
plane of "major activity" that could be clearly identified. Moreover,

such a scheme would again contradict the idea of standardization,
whether desirable or not.

In summary, then, it would appear that the arguments advanced in
support of the proposed ISB convention are not convincing. Also, the
opinion aired by the Editor-in-Chief of the Journal of Biomechanics,
Richard A. Brand, in his EDITORIAL COMMENT on the ISB
recommendations that these represent "a thoughtful approach..." and
"a compilation of commonly accepted practices" may not be shared by
too many biomechanists. In this context it is also noteworthy and
remarkable that responses from the members of the ISB Standards and
Terminology Commitee (notably from Ge Wu, Peter Cavanagh, John Paul,
Don Grieve, and others) were conspicuously absent from the present
discussion. The reasons for this strange silence remain clouded in
mystery and forces everyone into speculation.

To conclude, a rejection rate of 79% (in this discussion forum) for
proposed ISB convention does not augur well for future acceptance of
these standards. In my opinion, the ISB Standardization and
Terminology Committee would be well advised to withdraw the present
recommendations and revise them in accordance with internationally
accepted conventions and, most important, in collaboration with the
scientific community of biomechanists.

I thank all of you who have contributed to this discussion and
thereby to the clarification of an important issue.

Herbert Hatze, PhD.
Professor of Biomechanics
University of Vienna