Joint coordinate system overview.

Each joint is allowed 6 degrees of freedom (DOF) about an established coordinate system based on inertial axes of the downstream bone (e.g. humeral inertial axes determine glenohumeral axes). Joint rotations are ordered such that rotation about the blue axis moves the other two axes and bone model; rotation about green moves only the red axis and bone model; and rotation about the red axis only affects the bone model. Rotation order follows blue, green and red in each joint depicted. Cst = coracosternal joint: blue – abduction/adduction; green – protraction/retraction; red – long axis rotation. Sh = shoulder (glenohumeral), El = elbow, and Wr = wrist joints: blue – elevation/depression; green – protraction/retraction; red – pronation/supination. Note, none of the joints are depicted in their zero reference pose. For example, the elbow is extended 120 degrees from its zero position. Specifics for each joint are discussed in results. The * marks the distal-most point on the os phalanx distalis digiti used to determine upstroke and downstroke transitions.