Grade 0, normal muscle tone. Grade 1, slightly increased muscle tone: minimal resistance at the end of the range of motion of the joint during passive flexion and extension of the affected part, or sudden catch and release. Grade 1+, slight increase in muscle tone: sudden jamming within 50% of joint movement, then minimal resistance in the last 50% of the joint range of motion. Grade 2, more marked increase in muscle tone: The muscle tone increases more markedly through most of the range of motion of the joint, but the affected part can still be moved easily. Grade 3, severely increased muscle tone/difficulty in passive movement. Grade 4, stiffness: The affected part is stiff and immobile during passive flexion and extension.