ABSTRACT
A distinction is made between the terms “extension” and “hyperextension”. Extension is used when the motion opposite to flexion, at the zero starting position, is a natural motion. As the motion opposite to flexion at the zero starting position is an unnatural one, it is referred to as hyperextension[1]. However, the problem is how to determine which range of motion (ROM) is unnatural and which is natural, specially in joints with restricted extension ROM as the knee joint.
