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Florence Billet
08-28-2006, 06:10 PM
Dear Biomch-l readers,

I am implementing a biomechanical model and then I try to follow the ISB
recommendations for the joint coordinate systems of the various joints
of the body. I have read the following papers:

G. Wu, S. Siegler, P. Allard, C. Kirtley, A. Leardini, D. Rosenbaum, M.
Whittle, D. D’Lima, L. Cristofolini, H. Witte, O. Schmid, I. Stokes. ISB
recommendation on definitions of joint coordinate system of various
joints for the reporting of human joint motion – Part I: ankle, hip, and
spine. Journal of Biomechanics, 35(4):543-548, 2002

Wu G, van der Helm FC, Veeger HE, Makhsous M, Van Roy P, Anglin C,
Nagels J, Karduna AR, McQuade K, Wang X, Werner FW, Buchholz B;
International Society of Biomechanics. ISB recommendation on definitions
of joint coordinate systems of various joints for the reporting of human
joint motion--Part II: shoulder, elbow, wrist and hand. J Biomech. 2005
May;38(5):981-992. Review.

and I have some questions about the notations for the left parts of the
human body.


I understand the notations for the right parts of the body, but I
don't understand very well the notations for the left parts. For
example, for the right shoulder, the humerus coordinate system is well
defined and the positive rotations around these axis correspond to the
positive rotations defined by the direct frame (Xh, Yh, Zh).
For the left shoulder, it is said in the introduction that "When left
shoulders are measured, it is recommended to mirror the raw position
data with respect to the sagittal plane (z = -z). Then, all the
definitions for right shoulders are applicable".
Then, if we mirror the raw position data with respect to the sagittal
plane, we obtain the frame (Xh_l, Yh_l, Zh_l) where Xh_l points forward,
Yh_l is the line connecting GH and the midpoint of EL and EM, pointing
to GH (that is to say pointing upwards) and Zh_l pointing to the left.
But in this case, the frame (Xh_l, Yh_l, Zh_l) isn't direct. Then, how
the positive sense of rotations are defined? For example, the elevation
of the right shoulder (beta_h) is negative. For the left shoulder, this
elevation is negative or not?

Futhermore, I have the same problem for the lower limb joints. I
believe that the frames corresponding to the left leg joints all have X
axis pointing forward; then all Y axes are the lines joining the
midpoint between the medial and lateral femoral epicondyles and the hip
center of rotation and pointing upwards and Z axis pointing to the right
of the body. In this case, if we take the positive sense of rotations
defined by the direct frame (X, Y, Z), then we have for example a
positive internal-rotation for the right hip and a negative one for the
left hip.

Then, do the conventions follow this rule:
The mirror angles for the upper-limb joints have the same signs and the
mirror angles for the lower limb joints have opposite signs?

And if it isn't the case, which are the conventions used for the frames
and the rotation senses for the left parts of the body?

I hope I was clear enough...

Thank you for your attention,
Sincerely,
Florence Billet, BIPOP team, INRIA laboratory, France