# Spine rythmn matrix and LinCombMeasure

Hi,

[SIZE=2]I would like to get some more information about the spine rythmn. I know that you used the beam theory with the variing stiffness along the spine to calculate the deformations along it. But the values in the coefficient matrix of SRMatrix are not clear to me. Why did you use the valus “-1” and the values in the last three columns of the matrix.[/SIZE]
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[SIZE=2]Thanks a lot,[/SIZE]
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[SIZE=2]Best regards,[/SIZE]
[SIZE=2]Alex
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Hi Alex,

The SRMatrix is not a stiffness matrix as you may think. It represents the kinematic coefficients of the AnyKinMeasureLinComb.

This object creates linear equtions between several kinematic measure. So the coefficients of the matrix are the coeficients of the equations. In this case all the lumbar joints angles are calculated relative to the last one in the list T12L1Jnt.

So for example the first line of the matrix states that the first rotation of the SacrumPelvisJnt is 7.105616e-002 time the first rotation of T12L1Jnt:
{-1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7.105616e-002, 0, 0},

And so it goes for each dof.

I hope the explanation is clear enough. I also invite you to read the description of AnyKinMeasureLinComb in the reference manual.

Best regards, Sylvain.

Hi Sylvain,

how the the linear combination works is clear.
But where did you get this value 7.105616e-002 from and the other factors of the last three columns respectively? If these are percentual values of the distribution of the rotation between pelvis and thorax, then it would be too much. The next values in this column are 0.2276, 0.4020, 0.5784 and so on. So you will get 22.76% of the rotation in T12L1Jnt in SacrumL5Jnt, 40.20% of the rotation in T12L1Jnt in L5L4Jnt and so on? Or I didn’t understand how the AnyKinMeasurelinComb itself works. I assume these factors are calculated by solving the differential equations of the beam theory. Could you give some more explanations about these DE?

Best regards,
Alex

Hi Alex,
yes, the spine rhythm itself is based on the elastic beam theory. The components of the rhythm are used to give each degree of freedom as a percentage of the T12/L1 joint.
Here are some slides from validation experiments:
http://www.anybody.aau.dk/seatedhuman/Results3/Experiments_files/frame.htm
Best regards,
Sebastian