While the original Zatsiorsky-Seluyanov segment inertia parameters (1983) used bony landmarks as reference points, de Leva (1996) adjusted these parameters using joints centres instead, more commonly used in biomechanics. This page lists these adjusted parameters and describes how to used them in Visual3D.

The images below show the default segment properties on the left and the modified segment properties on the right. The modified segment properties reflect Zatsiorsky's adjusted segment properties for a female's right thigh.

ORIGINAL This is an example of the original properties using Hanavan's geometric model.

MODIFIED This is an example of the modified properties using De Leva's values.

1. Change the segment geometry to CUSTOM_SEG

2. To modify the Mass, replace the mass factor from the current equation (0.1* Mass) to Zatsiorsky-Seluyanov mass value(For example: “0.1478 * Mass” for a female thigh segment).

3. To modify the Inertia Values, the expression has to be entered as: “m*r^2”
Where m is the segment's mass parameter, and r is the IXX, IYY or IZZ radius of gyration parameter. The radius of gyration in De Lava's paper is presented as a percent of segment length, so this value must be multiplied by the length of the segment.

For example, to use the Zatsiorsky-Seluyanov's Inertia Values for the right thigh for a female subject, the following expressions would have to be entered in the IXX, IYY and IZZ fields.

IXX = ( 0.1478*Mass ) *((RTH_SEG_LENGTH * 0.369 )^2)
IYY = ( 0.1478*Mass ) *((RTH_SEG_LENGTH * 0.364 )^2)
IZZ = ( 0.1478*Mass ) *((RTH_SEG_LENGTH * 0.162 )^2)

4. To modify the location of the center of mass according to Zatsiorsky-Seluyanov's parameters, replace the factor from the current equation (0.444004 * RTH_Seg_Length in the above image) with the corresponding Centre of Mass location parameter (for example: “0.3612 * RTH_Seg_Length” for a female thigh segment).

The segment length (RTH_SEG_LENGTH) is listed under the Subject Data / Metrics tabs. This value is automatically created when a segment is created.

Visual3D's default segment parameters are derived from Dempster's 1955 equations.

• de Leva (1996) Adjustments to Zatsiorsky-Seluyanov's segment Inertia Parameters. Journal of Biomechanics Vol.29 No. 9. pp.1223-1230. DOI
• Dempster, W. T. (1955). Space requirements of the seated operator, geometrical, kinematic, and mechanical aspects of the body with special reference to the limbs (No. WADCTR55159) link
• Zatsiorsky, V. M., & Seluyanov, V. (1983). The mass and inertial characteristics of the main segments of the human body. In H. Matsui & K. Kobayashi (Eds.), Biomechanics VIII-B (pp. 1152-1159). Baltimore: University Park Press.