2. From measurement to interpretation: calculating joint kinematics

In human motion analysis, where the focus is on skeletal joints, it is customary to consider the human body as a mechanical system made up of rigid bodies – body segments then assumed to be dimensionally stable – articulated to each other. Depending on the application envisaged, we may, for example, in the case of the upper limb, assume that the thorax, arm, forearm and hand are rigid bodies articulated respectively by the shoulder complex, the elbow and the wrist, if we want a global analysis of the gesture; or break down the various bone segments and joints of the shoulder or hand complex in more detail in other cases...

Joint translations are often overlooked, not least because few non-invasive measurement systems are currently accurate enough to assess them correctly. Nevertheless, there are multiple solutions for expressing three-dimensional joint rotations,...