Fig. 2

The coordinate position of knee joint center (KJC) based on different knee flexion angle during static trials: α) 0°condition, β) 15°condition, γ) 30°condition. Note that difference in the coordinate position of KJC in relation to ankle joint center (AJC) was based on the different knee flexion angle during static trials, the 15° and 30° conditions resulted in an anterior, medial and distal translation. The Z-axis (blue) was defined by the vector from KJC to Hip joint center (HJC) (direction from distal to proximal, proximal as positive), the medial–lateral axis (red) (X-axis) was defined by the vector from KJC to medial femur epicondyles (direction from left to right, right as positive), the anterior–posterior axis (green) (Y-axis) was determined by the cross-product between the Z-axis and the X-axis (direction from posterior to anterior, anterior as positive).