Studies of the human stretch reflex.

We recorded the late electromyographic (EMG) responses to predictable and unpredictable stretches of the wrist flexor and extensor muscles during ballistic movement or isometric contractions. We simultaneously recorded the accompanying cerebral responses. Our findings suggest that the late EMG responses are influenced by suprasegmental (cerebral) phasic mechanisms that seem to have a dual functional role, being involved in the control of limb stiffness and in a servomechanism to return the displaced limb to its intended position.