Figure 2

A. Typical normal knee flexion-extension angular response showing onset angle, resting angle, the first three peak flexion angles (F1, F2, F3), the first three peak extension angles (E1, E2, E3), the period of the first cycle (T); B. pendulum test angular response for a patient mildly affected (class I, ACR classification); C: pendulum test angular response for a patient severely affected (class III, ACR classification). Abbr.: ACR (American College of Rheumatology)