Figure 1

(A) The ultrasound probe was equipped with a marker-cluster to transform the image coordinates to the motion-capture coordinate system. A marker-cluster placed at the sacrum of the participants served as the local reference system. (B) This image illustrates how the pixel coordinates of the bone surface, in this case of the anterior superior iliac spine (ASIS), in each ultrasound image were manually digitized. Note that for the identification of the ASIS location the most anterior point was selected manually.