Modify body size

[Shirley (Shirley Xu)]

Hi,
I found a phenomenon that I don't quite understand when trying to modify the body size. In this part, when I changed the LengthStandard to twice the original, I found that the length was not doubled, but shortened to half of the original. When I changed the MassStandard to twice the original size, I found that the shank became thinner instead of thicker. I don't really understand, so I want to ask you why.

Shank = {
  /// Based on the mass of TLEM1.2 but corrected with
  /// the ratio TLEM2/TLEM1 segment length ratio
  AnyVar MassStandard = 3.6287;
  AnyVar Density = 1000;
  AnyVar LengthStandardForFibers = 0.4098;//**used for fiber length scaling
  AnyVar LengthStandard = 0.5*(vnorm(..Seg.Shank.StdPar.KneeJoint-..Seg.Shank.StdPar.AnkleJoint)); 
  AnyVec3 sCoM =  (..Seg.Shank.KneeJoint.sRel-..Seg.Shank.ShankJoint.sRel)/2;

  AnyVar AnkleWidth =  0.0753;

  AnyVar Length = vnorm(..Seg.Shank.KneeJoint.sRel-..Seg.Shank.AnkleJoint.sRel);
  AnyVar Radius = (..Seg.Shank.Mass/(3.1416*Length*..StandardParameters.Shank.Density))^0.5;
  AnyVar Ixx = 0.25*..Seg.Shank.Mass*Radius*Radius + 1/12*..Seg.Shank.Mass*Length*Length;
  AnyVar Iyy = 0.5*..Seg.Shank.Mass*Radius*Radius;
  AnyVar Izz = Ixx;
  AnyMat33 JM=..Seg.Shank.ScalingNode.ARel*{{Ixx,0,0},{0,Iyy,0},{0,0,Izz}}*..Seg.Shank.ScalingNode.ARel';
  AnyVec3 Jii = {JM[0][0], JM[1][1], JM[2][2]};
  AnyVec3 Jij = {JM[1][0], JM[2][1], JM[2][0]};

};

Best regards.
Xu.

[dschander (Divyaksh S. Chander)]

Hi Xu,

I think what's happening is that the value you are changing is being used to calculate a scaling factor that is subsequently being used to scale the shank length. You are trying to change the value of the standard parameter length. This is the length from the actual cadaver study. Then, the anthropometrics file provides a desired length for the shank of the human model. Simply put, these two values are put together as a ratio (desired length / standard length) to find the scaling factor for the model. This scaling factor is used to actually scale the shank when it's loaded and assembled in the human model. So, when you double the standard length of the shank, you essentially halve the scaling factor and that is why you see the shank length reduced to half.

Hope this helps.

Best regards,
Dave