5.1.4 The forearm and lower leg segments

The forearm segment extends from the elbow to the wrist, while the lower-leg segment extends from the knee to the ankle. In the biomechanical model, both segments have a single degree of freedom: flexion/extension. Axial rotations of the forearm and lower leg are not assigned to these segments. Instead, they are represented in the next segment of the kinematic chain: by pronation/supination of the hand segment and abduction/adduction of the foot segment, respectively.