title: Step initiation in Parkinson's disease: influence of initial stance conditions.
abstract: In this study, we investigated how the size of preparatory postural adjustments prior to step initiation, and step length and velocity depend on initial stance width in patients with Parkinson's disease (PD) both in the ON and OFF levodopa states and in healthy elderly subjects. Twenty-one subjects with idiopathic PD and 24 age-matched healthy control subjects took two steps starting with feet on a two-plate force-platform, from either narrow or wide stance width. We measured how the magnitude of anticipatory postural adjustments (APA) and step characteristics scaled with stance width. Results showed that preparation for step initiation from wide stance was associated with a larger lateral and backward center of pressure (CoP) displacement than from narrow stance. Velocity and length of the first step were also sensitive to initial stance conditions, probably in relation with the differences in the corresponding APA. On the contrary, the duration of APA was not significantly affected by initial stance width, but it was longer in PD compared to healthy subjects, and speeded up by levodopa. Although subjects with PD did scale up the size of their APA with stance width, they had much more difficulty initiating a step from a wide stance than from a narrow stance, as shown by the greater differences from control subjects in the magnitude of the APA. Our results support the hypothesis that PD subjects maintain a narrow stance as a compensation for their inability to sufficiently increase the size of their lateral APA to allow fast step initiation in wide stance.
authors.affiliation: Biomedical Engineering Unit, Department of Electronics, Computer Science & Systems, University of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy. lrocchi@deis.unibo.it
authors.forename: Laura
authors.initials: L
authors.lastname: Rocchi
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Chiari
authors.forename: Martina
authors.initials: M
authors.lastname: Mancini
authors.forename: Patricia
authors.initials: P
authors.lastname: Carlson-Kuhta
authors.forename: Anne
authors.initials: A
authors.lastname: Gross
authors.forename: Fay B
authors.initials: FB
authors.lastname: Horak
mesh_terms: D000368:Aged; D000978:Antiparkinson Agents / Q000627:therapeutic use; D001479:Basal Ganglia / Q000187:drug effects / Q000503:physiopathology; D005260:Female; D005684:Gait / Q000187:drug effects; D020233:Gait Disorders, Neurologic / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology*; D006801:Humans; D007866:Leg / Q000294:innervation / Q000503:physiopathology; D007980:Levodopa / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D009434:Neural Pathways / Q000187:drug effects / Q000503:physiopathology; D010300:Parkinson Disease / Q000175:diagnosis / Q000188:drug therapy / Q000503:physiopathology*; D004856:Postural Balance / Q000187:drug effects
chemical_list: D000978:Antiparkinson Agents; D007980:Levodopa