The Result of Mid-High-Heeled Footwear on Young Adult Women
u vertical balance angle ( vertical trunk inclination in the sagittal plane )( VBA ), which is the angle between the vertical axis and the line connecting C7 and IF , the positive value corresponds to the subject leaning forward ,
u thoracic kyphosis angle ( TKA ), which is the angle between normal vectors of planes fitted in the area around points C7 and ThK-LL , with an additional offset to C7 equal to 5 mm in the direction of ThK-LL ,
u lumbar lordosis angle ( LLA ), which is the angle between normal vectors of planes fitted in the area around points IF and ThK-LL , with an additional offset to IF equal to 15 mm in the direction of ThK-LL ,
u pelvic inclination angle ( PIA ), which is the angle between the normal vector of the plane fitted to the area between LVD and RVD and the horizontal axis .
All the vectors were projected onto the sagittal plane before calculating the angles . Additional markers at the left and right scapula ( LSC , RSC ), left and right axilla ( LAX , RAX ) and the deepest point of lumbar lordosis ( LL ) were used to calculate the parameter for determining possible faulty posture :
u the Suzuki Hump Sum ( SHS ) [ 64 , 65 , 66 ] , calculated as the sum of the difference in depth between points of contact of lines in the axial plane tangent with the surface of the back , on three different levels : halfway between LSC and RSC , at ThK-LL and LL
The principles of extracting all the parameters are presented in Figure 4 . Out of the angles used for monitoring posture change , calculated for the three measurements without heels for each subject , the average value was calculated and used as the reference . The exclusion criterion was based on the SHS parameter . Although this parameter is well established in Surface Topography ( ST ) measurements [ 26 , 27 , 60 , 65 , 66 , 67 , 68 ] , literature does not provide specific cut-off values for faulty posture . Thus , subjects with outlier values of the SHS distribution in any of the measurements were suspected of having a faulty posture and were excluded from the study . This parameter was used only as a base for exclusion and was not used in further analysis .
2.9 . Influence of Marker Placement Accuracy
The position of attached fiducial markers affects directly the calculated parameters . Additional analysis was performed to test the influence of their position on the obtained results . The procedure was as follows :
u for each subject , for each landmark , draw a random displacement vector from the N ( 0 , 10 ) distribution , each vector component was drawn independently ,
u after applying the displacement vector to each landmark , the point was projected to the cloud to find a real point on the surface .
The random displacement vector was constant for each subject . This is equivalent to a different marker placement throughout the whole session . The values of parameters were calculated again for the new set of markers , and the results were statistically analyzed . The procedure was repeated ten times and was performed for parameters , which were statistically significant for the original marker positions . Three runs of application of marker displacement vectors for one measurement is shown in Figure 5 .
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