Stretch reflex of quadriceps femoris and its relation to rigidity in Parkinson's disease

Much evidence suggests that parkinsonian rigidity is due to hyperactivity of a reflex arc. While tendon jerk and H reflex are not modified in Parkinson's disease (PD), the long-latency component of strech reflex (LLR) shows an increased sie in PD. It has been proposed that this modification could account for rigidity. We studied in 14 PD patients and 8 normal subjects the stretch reflex of the quadriceps femoris. The muscle was streched by a torque motor in two experimental set: at rest and with voluntary background activity