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    Guest replied
    ISB STANDARDIZATION RECOMMENDATION

    SUBJECT: ISB STANDARDIZATION RECOMMENDATION

    The standardization proposals recently made by Yeadon/Bogert/Legnani
    (16 October) and endorsed by J. Dapena (19 Oct.), are in full
    agreement with my original proposal of 28 September 1995 concerning
    the use of Cardan angles to describe 3D whole-body and segment
    orientation, and the use of the internationally accepted 3D coordinate
    system XYZ. In fact, my three-dimensional 17-segment human body
    model first published in 1980 ("A mathematical model for the
    computational determination of parameter values of anthropomorphic
    segments", J. of Biomechanics 13, 833-843) and then used repeatedly
    in subsequent papers ("Neuromusculoskeletal control systems modeling -
    a critical survey of recent developments", IEEE Transactions on
    Automatic Control AC-25, 375-385, 1980, "HOMSIM: a simulator
    of three-dimensional hominoid dynamics", CSIR - Special Report
    SWISK 23, 1981, "Computerized optimization of sports motions: an
    overview of possibilities, methods and recent developments", J. of
    Sports Sciences 1, 3-12, 1983, etc.) already employs Cardan angles
    for describing 3D whole-body and segment orientations and, as
    spatial and segmental coordinate system, a Cartesian XYZ reference
    frame with the X-axis pointing towards the PASSIVE observer (or
    to the right of the subject IF THE PLANE OF FORWARD
    PROGRthe right of the PASSIVE observer (or in the direction of the
    subject moving forward in the sagittal plane), and the Z-axis normal
    to the other two axes in a right-handed Cartesian coordinate system.

    My reasons for selecting Cardan angles (also called Bryant angles)
    were similar to those of Fred Yeadon and Jesus Dapena. While the
    critical case (gimbal lock) occurs for Cardan angles at PHI2=PI/2+n*PI
    (n=0,1,2,...), this is the case at THETA=n*PI (n=0,1,2,...) for Euler
    angles. However, for most situations arising in biomechanics it is
    more advantageous to have the critical case occurring at a larger
    angle and not near THETA=0. This makes also possible the derivation
    of particularly simple expressions for the elements of a Cardan
    transformation matrix for the case where all three angles are near
    zero, which can not be done if Euler angles are used. This was an
    additional reason why I selected Cardan angles.

    As far as the XYZ labelling of the spatial and segmental coordinate
    axes is concerned, the overriding criterion for me was to adhere
    to internationally accepted norms. As already pointed out in my
    original e-mail of 28 Sept. 1995, this implies that the XYZ-axes
    system described above and also agreed upon by Yeadon, Bogert,
    Legnani, Dapena, and many others be used. Exceptions to this
    standard should be possible for specific purposes.

    I might also mention that I have sent summaries of the present
    ISB-standardization e-mail discussions to Dr. R. Brand in his
    capacity as editor of the Journal of Biomechanics. I am sure that he
    also wants to contribute to the present discussion.

    Herbert Hatze, Ph.D.
    Professor of Biomechanics, University of Vienna

    Leave a comment:


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    Guest replied
    Re: ISB Standardisation Document

    To the Biomch-L readership:

    I agree wholeheartedly with the Yeadon/Bogert/Legnani
    counterproposal for standardization.

    Comment #1: Cardan angles in the order X-Y-Z (i.e., successive
    rotations about the mediolateral, anteroposterior and longitudinal axes)
    should be a good and logical way to express segment orientations. I believe
    that this should be the "standard", which should be used ***almost***
    always. At the same time, we have to keep in mind that such an order (like
    any other order) will produce "gimbal lock" at certain orientations. (This
    is where some of the angles "go crazy" because there are two very different
    combinations of numerical values of the three angles that produce very
    similar physical orientations of the segment.) Gimbal lock should be
    avoided. A different Cardan angle order will achieve this. That is why I
    consider it very important also that the new proposal allows for deviations
    from the standard when necessary. There is no angle order that will prevent
    gimbal lock everywhere. Any angle order has a "ugly orientation" that
    produces gimbal lock. That is why we should not force any given order on
    every situation.

    Comment #2: I would like to recommend that the X axis generally
    should point toward the right, and the Y axis forward, instead of the
    alternative (X axis forward and Y axis toward the left). This is not really
    a very critical issue, but here is why I think that X toward the right and Y
    forward is somewhat better:

    When I am analyzing a person walking or running forward, I generally
    think of myself as an observer that is traveling with the subject. I feel
    that this helps me to gain a more intuitive understanding of what the
    subject is experiencing. When I am considering the values of forces or
    velocities in the horizontal plane, I think of myself as the subject looking
    downward at this plane. Then, if I am using the X=right/Y=forward
    convention relative to the direction of motion, when I look at the ground I
    will see the positive X direction pointing toward the right and the positive
    Y direction pointing forward, which is how I generally draw these axes when
    I make any graph on a piece of paper: I am in familiar territory. But if I
    use the alternative convention X=forward/Y=left, then when I look at the
    ground I see the X direction pointing forward and the Y pointing toward the
    left, which is more unfamiliar. I think most people would probably feel
    more comfortable with X=right/Y=forward.

    Jesus Dapena

    Leave a comment:


  • Guest's Avatar
    Guest replied
    Standardization and the ISB - Clean version

    The following message was corrupted during a Mac to Eudora transfer.=
    Here
    is a 'clean' version:

    ----------------------
    Dear Biomch-L readers:

    It has been rewarding to see the discussion over the last two weeks
    regarding the ISB Recommendations for Standardization in the Reporting=
    of
    Kinematic Data. This shows that there is a continued interest in=
    this
    area, which is why the ISB has moved forward with this project. =
    The vigor
    of the responses that this topic seems to engender may come as a=
    surprise
    to some new readers, but I can assure you that this is indeed "par=
    for the
    course". Any venture into the area of standardization is definitely=
    not
    for the faint-hearted!

    The Recommendation (J. Biomech pp 1257-1260, October 1995) evolved=
    through
    many versions, and has been developed based on consideration and=
    comment
    from members of the ISB and from readers of this list. The first=
    public
    airing of the proposed recommendation was at the XIIIth Congress=
    of the
    International Society of Biomechanics, December 9-13, 1991, in Perth,
    Australia. On behalf of the committee, I presented an outline of=
    the
    proposed recommendation to approximately 300 ISB members. A lively
    discussion ensued and the comments were incorporated into Draft version=
    4.0
    which was reproduced in the February/March ISB Newsletter #45. BIOMCH-L
    readers may want to consult the BIOMCH-L archives for May 4, 1992,=
    where
    the draft was also posted to all subscribers. Comment was invited=
    and a
    summary of the comments received was published in the ISB Newsletter=
    #47
    Aug/Sept 1992. After two further drafts, the recently published
    Recommendation emerged. Those of you who missed the earlier posting=
    might
    find this a good reason (one of many!) to join the ISB in order to=
    keep
    abreast of these and other current issues.

    It is worth noting that a number of other groups such as the Scoliosis
    Society, the CAMARC group, the Clinical Gait Analysis Group are also
    working on standards and ISB maintains working relationships with=
    all of
    these groups. There is also a listing under "Standardization" on=
    the
    Biomechanics Home Page (http://dragon.acadiau.ca/~pbaudin/biomch.html)
    which at present points only to ISO. The soon to be released ISB=
    home page
    will also contain complete details of existing, proposed, and in=
    progress
    Recommendations and Standards from the ISB.

    The debate in the last two weeks has reiterated some of the issues,=
    and
    reinforced some of the motivations, that led to the pursuit of a=
    standard
    form of reporting that is specific to Biomechanics:

    =80 Within our own field, many different conventions are used for=
    reporting
    kinematic information so that the reader of each paper has to start=
    by
    working out which were used by the author (and perhaps holding graphs
    upside down or in a mirror!)

    =80 Outside our field, we find that there is indeed a number of different
    systems for describing the SAME thing. Each of the various sub-disciplines
    consider their method to be "standard". =20

    =80 We all tend to be very resistant to change from what we have=
    used in the
    past as "standard".

    =80 We have a tendency, if doing more complex analysis, to suggest=
    that the
    needs of those doing less complex analysis are less important.

    =46rom these reasons, the Recommendation was born. A key phrase=
    in the title
    of the Recommendation is "for the reporting of". The notion here=
    is that
    no one should have to use a system of computation that they are not
    comfortable with or simply do not like. However, once the results=
    are to
    be communicated to others, then there is a real need for standardization.=
    =20
    Converting to the ISB axis system could be seen as applying a filter.=
    The
    input of the filter is specific to each user while the output is
    understandable to all. This goes not just for the direction of the
    coordinate axes, but also for such things as the conventions used=
    for
    flexion/extension etc.

    The ISB exists for its members, and standardization is something=
    that
    members have asked us to pursue. No recommendation is cast in stone=
    and we
    will always move in a direction that the majority of our almost 1000
    members are comfortable with. We welcome input from all quarters=
    but we
    ask you to realize that any decision will leave in its wake a significant
    number of disaffected individuals who simply like the way they are=
    doing
    things at present.=20

    As the debate continues, those of you who feel so inclined might=
    try using
    the ISB conventions in reporting your data. =20


    Peter R. Cavanagh
    ISB President

    -----------------





    /-------------------------------\
    | Peter Cavanagh |
    | Center for Locomotion Studies |
    | Penn State University |
    | University Park |
    | PA 16802 USA |
    | -x- | =20
    | Voice +1 814 865 1972 |
    | FAX +1 814 863 4755 |
    | Email PRC@PSU.EDU |
    \_______________________________/

    Leave a comment:


  • Guest's Avatar
    Guest replied
    ISB Standardisation Document

    The following message is the outcome of email discussions on the topic of
    standardisation by Fred Yeadon, Ton van den Bogert and Giovanni Legnani.
    Since the standardisation proposal is "on the table" interested parties
    should (a) accept it as it stands (b) propose changes. We think that changes
    are needed and as an initial step have made some comments on the proposal.

    Comments on the document:

    Standardization and Terminology in Biomechanics.
    Volume 1. Section A.
    Recommendations for standardization in the reporting of kinematic data.

    It should be borne in mind that the purpose of standardisation is to have a
    common convention for REPORTING data so that the results of different
    researchers can be interpreted and compared more easily. Any discussion on
    this document should bear this in mind and avoid issues of what conventions
    are best used for data analysis. It is the reporting of results that is the
    present focus of the standardisation document.

    In the "Recommendations" document:-

    Part 1. X, Y, Z axes for displacements

    It should be recognised that there IS general agreement on the directions of
    the three Cartesian axes in that they are mutually perpendicular, one axis is
    vertical, and the directions of the remaining two horizontal axes are not
    usually contentious. There is some disagreement as to the NAMING (XYZ) of the
    three axes. There is also the issue of the senses of the axes in that there is
    general agreement that "up" is positive whereas "left" may be positive or
    negative. The system proposed in the standardisation document seems to be
    supported by people who have initially used 2D analysis and have added the a
    horizontal Z axis for 3D in order to preserve consistency between 2D and 3D.

    Unfortunately the majority of researchers in biomechanics seem to favour a
    system in which the Z axis is vertical. This does not augur well for the
    acceptance of the standardisation proposal in its present form.

    However, since there is general agreement on the directions of the axes and the
    focus is on the reporting of data, standardisation could take the form of naming
    these axes with words rather than with letters. For example, it might be
    possible to use "forward", "lateral", and "vertical" to name these directions.
    The point is not that particular names be cast in stone but that it become
    common practise to use appropriate words rather than XYZ.

    Another issue is that the XYZ system used should fit well with the system used
    to describe rotations. This will be addressed after the comments on Part 4 and
    Part 5.

    Part 2. Definition of segmental reference frames

    The system proposed in the standardisation document is consistent with the
    system proposed for the absolute reference frame in Part 1. However, as noted
    above, most researchers are not in agreement with the adoption of the proposed
    Part 1. An alternative will be proposed after considering relative orientation
    in Part 5.


    Part 4. Absolute Orientation

    In the standardisation document it is proposed that the absolute orientation of
    a body segment be defined by successive rotations about lateral, longitudinal
    and frontal axes. Since the system for defining the orientation of the whole
    body has not yet been published the present proposal prejudges the issue.
    Recommendations have been made to the Standardization Committee on whole body
    orientation as detailed in:

    Yeadon, M.R. 1990. The simulation of aerial movement. Part I: The determination
    of orientation angles from film data. Journal of Biomechanics 23, 59-66.

    In this system successive rotations are made about the lateral, frontal and
    longitudinal axes. This order of rotations has the advantage that the Cardan
    angles of somersault, tilt and twist agree with the nomenclature used by
    gymnasts and coaches. Since the focus is on the reporting of data such
    considerations of the established use of terminology are of great relevance.

    Part 5. Relative Orientation

    The description of the system proposed here appears to be somewhat ambiguous but
    our interpretation is that successive rotations about lateral, frontal and
    longitudinal axes bring one segment from initial alignment with a more proximal
    segment to its final relative orientation. That is we interpret the proposal
    as stating that the system described in the cited publication (Grood and Sunday,
    1983) is to be adopted. If this is so then we are in agreement with this part
    of the proposal and expect that most researchers will also find it acceptable.
    On the other hand this definition is in conflict with that proposed in Part 4,
    suggesting again that Part 4 be changed.

    Part 1 and Part 2.

    It would be attractive to think that articles could use Tables in which axes
    were labelled with words rather than X, Y and Z but since this is unlikely to
    occur there is a case for having a standard system. One rationale would be to
    let the definition of orientation dictate the axes nomenclature by requiring
    sequential rotations about the X, Y and Z axes. This leads to the adoption of
    a system with Z vertical (longitudinal).

    One final note of caution on the subject of standardisation:

    There is a danger if recommendations were to be adopted formally by an academic
    journal. Any standardised system will need to be able to adapt to various needs
    and changing circumstances. For different types of arm movements it may be
    helpful to use different systems of describing orientation. It will not be
    helpful if systems are cast in stone from on high. Researchers need the freedom
    to choose what they think is best bearing in mind the conventions prevalent at
    the time. For example even if whole body orientation is "standardised" in some
    way, it should not be imposed on all activity. What is a sensible system for
    gymnastics may not necessarily be sensible for high jumping. It should rest
    with the researchers of high jumping to arrive at a useful system bearing in
    mind what already exists.

    Fred Yeadon
    Ton van den Bogert
    Giovanni Legnani

    --
    M.R. (Fred) Yeadon
    M.R.Yeadon@lut.ac.uk

    Leave a comment:


  • Guest's Avatar
    Guest replied
    Standardization and the ISB

    Dear Biomch-L readers:

    It has been rewarding to see the discussion over the last two weeks
    regarding the ISB Recommendations for Standardization in the Reporting=
    of
    Kinematic Data. This shows that there is a continued interest in=
    this
    area, which is why the ISB has moved forward with this project. =
    The vigor
    of the responses that this topic seems to engender may come as a=
    surprise
    to some new readers, but I can assure you that this is indeed "par=
    for the
    course". Any venture into the area of standardization is definitely=
    not
    for the faint-hearted!

    The Recommendation (J. Biomech pp 1257-1260, October 1995) evolved=
    through
    many versions, and has been developed based on consideration and=
    comment
    from members of the ISB and from readers of this list. The first=
    public
    airing of the proposed recommendation was at the XIIIth Congress=
    of the
    International Society of Biomechanics, December 9-13, 1991, in Perth,
    Australia. On behalf of the committee, I presented an outline of=
    the
    proposed recommendation to approximately 300 ISB members. A lively
    discussion ensued and the comments were incorporated into Draft version=
    4.0
    which was reproduced in the February/March ISB Newsletter #45. BIOMCH-L
    readers may want to consult the BIOMCH-L archives for May 4, 1992,=
    where
    the draft was also posted to all subscribers. Comment was invited=
    and a
    summary of the comments received was published in the ISB Newsletter=
    #47
    Aug/Sept 1992. After two further drafts, the recently published
    Recommendation emerged. Those of you who missed the earlier posting=
    might
    find this a good reason (one of many!) to join the ISB in order to=
    keep
    abreast of these and other current issues.

    It is worth noting that a number of other groups such as the Scoliosis
    Society, the CAMARC group, the Clinical Gait Analysis Group are also
    working on standards and ISB maintains working relationships with=
    all of
    these groups. There is also a listing under "Standardization" on=
    the
    Biomechanics Home Page (http://dragon.acadiau.ca/~pbaudin/biomch.html)
    which at present points only to ISO. The soon to be released ISB=
    home page
    will also contain complete details of existing, proposed, and in=
    progress
    Recommendations and Standards from the ISB.

    The debate in the last two weeks has reiterated some of the issues,=
    and
    reinforced some of the motivations, that led to the pursuit of a=
    standard
    form of reporting that is specific to Biomechanics:

    =80 Within our own field, many different conventions are used for=
    reporting
    kinematic information so that the reader of each paper has to start=
    by
    working out which were used by the author (and perhaps holding graphs
    upside down or in a mirror!)

    =80 Outside our field, we find that there is indeed a number of different
    systems for describing the SAME thing. Each of the various sub-disciplines
    consider their method to be "standard". =20

    =80 We all tend to be very resistant to change from what we have=
    used in the
    past as "standard".

    =80 We have a tendency, if doing more complex analysis, to suggest=
    that the
    needs of those doing less complex analysis are less important.

    =46rom these reasons, the Recommendation was born. A key phrase=
    in the title
    of the Recommendation is "for the reporting of". The notion here=
    is that
    no one should have to use a system of computation that they are not
    comfortable with or simply do not like. However, once the results=
    are to
    be communicated to others, then there is a real need for standardization.=
    =20
    Converting to the ISB axis system could be seen as applying a filter.=
    The
    input of the filter is specific to each user while the output is
    understandable to all. This goes not just for the direction of the
    coordinate axes, but also for such things as the conventions used=
    for
    flexion/extension etc.

    The ISB exists for its members, and standardization is something=
    that
    members have asked us to pursue. No recommendation is cast in stone=
    and we
    will always move in a direction that the majority of our almost 1000
    members are comfortable with. We welcome input from all quarters=
    but we
    ask you to realize that any decision will leave in its wake a significant
    number of disaffected individuals who simply like the way they are=
    doing
    things at present.=20

    As the debate continues, those of you who feel so inclined might=
    try using
    the ISB conventions in reporting your data. =20


    Peter R. Cavanagh
    ISB President

    Leave a comment:


  • Guest's Avatar
    Guest replied
    ISB RECOMMENDATIONS FOR STANDARDIZATION

    SUBJECT: ISB RECOMMENDATIONS FOR THE STANDARDIZATION
    OF THE REPORTING OF KINEMATIC DATA - RESUME OF
    THE BIOMCH-L DISCUSSION FORUM OPENED BY
    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
    conventions.

    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
    pertain
    to the opinion expressed by Hamid Rassoulian ("the plane of
    progression
    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
    a
    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
    most
    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
    the
    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

    Leave a comment:


  • Guest's Avatar
    Guest started a topic ISB Recommendation for Standardization

    ISB Recommendation for Standardization

    Subject: DISCUSSION-FORUM on the ISB Recommendations for
    Standardization in the Reporting of Kinematic Data

    In the October-1995 issue of the Journal of Biomechanics appeared on
    pages 1257-1260 the "ISB RECOMMENDATIONS FOR STANDARDIZATION IN THE
    REPORTING OF KINEMATIC DATA" presented by G. Wu and Peter R. Cavanagh
    on behalf of the ISB-Standardization and Terminology Committee. The
    recommendations are followed by an EDITORIAL COMMENT written by R.A.
    Brand.

    Among other proposed definitions are the recommended directions of the
    global (resp. local segmental) right-handed Cartesian axes: the
    +Y-axis pointing upward and parallel with the field of gravity
    (+Yi-segmental axes pointing towards the proximal joint of a
    segment), the +X-axis pointing in the forward direction to the right
    (the +Xi-axes in the anterior direction), and the +Z-axis sidewards
    and perpendicular to the XY-plane (and similarly the +Zi-axes).

    This proposed convention ignores and contradicts all international
    standards and commonly accepted practices in physics, mechanical
    engineering, Lagrangian dynamics, applied mathematics and, most
    important, also in biomechanics. The following spatial (and hence also
    segmental) Cartesian coordinate system(s) is (are) commonly adopted:
    the X-axis points sidewards (in the direction of the ISB-proposed
    Z-axis), the Y-axis in the forward direction, and the Z-axis upwards
    in the vertical direction.

    Here follows a small sample of English (American)-language and
    internationally renowned textbooks and works in which this spatial
    coordinate system is used: L.K. Branson:ENGINEERING MECHANICS, Simon
    and Schuster, New York, 1970, p. 3; R.Resnick and D. Halliday:
    PHYSICS (parts I and II), John Wiley, New York, 1966, p. 302; D.A.
    Wells: LAGRANGIAN DYNAMICS, Schaum Publ., New York, 1967, p. 181; H.
    Goldstein: CLASSICAL MECHANICS, Addison-Wesley, 1969, p. 94; J.L.
    Synge, B.A. Griffith: PRINCIPLES OF MECHANICS, Mc Graw-Hill, New
    York, 1959; P. Allard, I.A.F. Stokes, J. Blanchi: THREE-DIMENSIONAL
    ANALYSIS OF HUMAN MOVEMENT, Human Kinetics, 1995, p. 147; J.
    Wittenburg: DYNAMICS OF SYSTEMS OF RIGID BODIES, Teubner, Stuttgart,
    1977, p. 21.

    I am unable to understand why the ISB can make recommendations which
    not only grossly contradict international standards but also ignore
    the e-mail discussions of a few years ago, in which a number of
    colleagues (including me) proposed this universally accepted
    coordinate system which has already been used in the creation of
    three-dimensional human body models. In addition, the ISB-recommended
    coordinate system necessitates an awkward sequence of rotations in
    obtaining the rotation matrix: rotation about the Z-axis first,
    followed by Y and X, while the common and logical sequence is (e.g.
    for Cardan angles) X, Y, Z. Finally, it should be pointed that most
    manufacturers of force plates also use this reference frame for
    defining ground reaction force components.

    Any biomechanist, who uses the ISB-proposed coordinate system in
    publications submitted to international engineering, mechanics,
    mathematics or similar journals runs the risk of being heavily criticized
    for not adhering to international conventions.

    I feel that this issue is certainly worth being discussed in this
    forum. In fact, in my opinion, it would have been wiser to discuss the
    ISB-recommendations within the scientific community before their
    publication in the Journal of Biomechanics.

    H. Hatze, Ph. D.
    Professor of Biomechanics, University of Vienna, Austria.
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