They assess patient improvement based on increases in range of joint motion and muscle strength. All motions of a joint are measured from defined zero starting point positions. The degrees of motion of a joint are added in the direction the joint moves from the zero starting position. Motions are described as active or passive. Active motion is the patient's movement of the joint through a specified arc of motion.
Passive motion is the examiner's movement of the joint through a special fled arc of motion.
A distinction is made between the terms extension and hyperextension. Extension is the natural motion opposite to flexion at the zero starting position. This is present in wrist and shoulder joints. If, however, the motion opposite to flexion at the zero starting position is an unnatural one, such as that of the elbows or knees, it is referred to as hyperextension. Limitation of joint motion is described simply.