Herbert Hatze

09-27-1995, 11:10 PM

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.

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.