title: Feedforward postural adjustments in a simple two-joint synergy in patients with Parkinson's disease.
abstract: Patients with Parkinson's disease, age-matched controls and young control subjects performed discrete elbow or wrist movements in a sagittal plane under the instruction to move one of the joints "as fast as possible." Relative stability of the other, postural joint was comparable in all 3 groups, while movement time was the highest in the patients and the lowest in young controls. Typically, EMG patterns in both muscle pairs acting at the joints demonstrated a commonly observed "tri-phasic" pattern. A cross-correlation analysis of the EMGs confirmed virtually simultaneous bursts in the wrist and elbow flexors and in the wrist and elbow extensors. In all 3 groups, there were no signs of anticipatory activation of postural muscles in about 90% of movements. We consider postural anticipation not a separate process, but a separate peripheral pattern of a single control process that may involve a number of joints and muscles. We conclude that the postural deficits in Parkinson's disease are not related to a basic deficit in the ability to generate feedforward postural adjustments but to other factors that may include the specificity of maintaining the vertical posture in the field of gravity.
authors.affiliation: Department of Physical Medicine and Rehabilitation, Rush-Presbyterian St. Luke's Medical Center, Chicago, IL 60612, USA.
authors.forename: M L
authors.initials: ML
authors.lastname: Latash
authors.forename: A S
authors.initials: AS
authors.lastname: Aruin
authors.forename: I
authors.initials: I
authors.lastname: Neyman
authors.forename: J J
authors.initials: JJ
authors.lastname: Nicholas
authors.forename: M B
authors.initials: MB
authors.lastname: Shapiro
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D004551:Elbow Joint / Q000503:physiopathology; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000503:physiopathology*; D011187:Posture / Q000502:physiology*; D014955:Wrist Joint / Q000503:physiopathology