Rotations of the humerus in the human shoulder girdle are usually described using five classical medical definitions: flexion/extension, abduction/adduction, internal/external rotation, horizontal abduction/adduction, and horizontal flexion/extension. The latter two are needed to overcome the inability of the first three to define the full range of motion. The International Society for Biomechanics recommendations reduce these to three sequential rotations around perpendicular axes: rotation of the plane of elevation (horizontal rotation), elevation, and axial rotation. We expand on this work by providing a new and intuitive visualization method to display these rotations that superimposes the axial rotation on the map projection of the reachable workspace of the elbow. We provide methods to interpret and create the visualization using direct observations, but also the equations and Matlab scripts needed to use the method. The visualization allows the immediate observation of the full rotational range of motion of the humerus and the interaction effects between these physiologically coupled rotations. Furthermore, it allows visualization of the effects of kinematic limitations of external devices such as endpoint manipulators or exoskeletons. Therefore, the new visualization method is useful for both clinical diagnostics and device development.
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