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

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