Associated postural adjustments in Parkinson's disease.

Postural activity in muscles of the back and legs associated with voluntary forward elevation of the arm at the shoulder with the subject standing was examined in 14 patients with Parkinson's disease and nine normal individuals.The time of onset of EMG activity in each of the postural muscles, relative to the onset of activity in the prime mover, was the same for both patient and normal groups and did not depend on load.The amplitude of the EMG bursts and their frequency of occurrence, was less in patients o drug treatment and immobile, than when mobile on therapy.We conclude that the timing of associated postural adjustments is normal in Parkinson's disease, although their size may be decreased.Patients with Parkinson's disease lose their balance more easily and fall over more frequently than do normal subjects.However, it is not known to what extent such postural instability reflects deficits in the "feedforward" (or programmed) adjustments of pos- ture which precede activation of the prime mover' or in "feedback" (or reflex) mechanisms of compen- sation.There is some evidence that feedback mech- anisms may be compromised in Parkinson's disease.Traub et al' found that anticipatory postural reflexes in leg muscles, produced by small, unexpected, dis- placements of the arm, were smaller in patients with Parkinson's disease than in normal controls.However, although there was a tendency for the patients who were more severely affected clinically to have the smallest postural reflexes, there were a number of very unstable patients whose postural reflexes were rela- tively normal.The conclusion was that although impairment of these reflexes may contribute to pos- tural instability, there must be other factors which contribute to the imbalance of patients with Parkin- son's disease.Previous reports of feedforward responses in Parkinson's disease3 have suggested an abnormality of the timing of postural EMG bursts relative to the