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    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