Figure 2

Anatomical coordinate systems and zero-positions of rotations are used to quantify three-dimensional kinematics of the pectoral girdle. The anatomical coordinate systems were placed in the center of rotation (c.o.r.) of the proximally adjacent joint (in case of 1^st thoracic vertebra into the center of the vertebral body; in case of scapula we approximated the instantaneous c.o.r. at the vertebral border of the scapula at the extension of the spina scapulae). X-axes (red) were set to represent the long axis of elements. Z-axes (blue) were oriented to represent the most distinct motion of the bone of interest. Y-axes (green) were orthogonal to the other two axes. For zero-points of rotations the anatomical axes were aligned according to the global coordinate system (unnatural pose). Motions of hierarchically higher elements have displacing effect for all lower ranked elements, i.e., motions of humerus are reported relative to scapula, scapular and clavicular motion relative to 1^st thoracic vertebra, 1^st thoracic vertebra motion relative to global reference.