title: Physiological mechanisms of rigidity in Parkinson's disease.
abstract: Electromyographic responses of triceps surae and tibialis anterior produced by dorsiflexion stretch were studied in 17 patients with Parkinson's disease. Most patients showed increased muscular activity when attempting to relax. A few patients showed an increase of short-latency reflexes when relaxed and when exerting a voluntary plantarflexion prior to the stretch. Many patients showed long-latency reflexes when relaxed and all but one showed long-latency reflexes with voluntary contraction; and these reflexes were often larger in magnitude and longer in duration than those seen in normal subjects. Unlike the short-latency reflex, the long-latency reflex did not disappear with vibration applied to the Achilles tendon. The long-latency reflexes and continuous responses to slow ramp stretches were diminished at a latency similar to the beginning of long-latency reflexes when the stretching was quickly reversed. Dorsiflexion stretch also frequently produced a shortening reaction in tibialis anterior. Of all the abnormal behavior exhibited by the Parkinsonian patients only the long-latency reflex magnitude and duration correlated with the clinical impression of increased tone. The mechanism of the long-latency reflex to stretch which is responsible for rigidity is not certain, but the present results are consistent with a group II mediated tonic response.
mesh_terms: D000328:Adult; D000368:Aged; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D009127:Muscle Rigidity / Q000503:physiopathology; D009132:Muscles / Q000294:innervation; D010300:Parkinson Disease / Q000503:physiopathology*; D011930:Reaction Time / Q000502:physiology; D012026:Reflex, Stretch; D014732:Vibration