title: Switching of movement direction is central to parkinsonian bradykinesia in sit-to-stand.
abstract: Patients with Parkinson's disease (PD) are known to manifest slowness in movements. We sought to identify the particular kinematic and kinetic disorders that contribute to the slowness in performing sit-to-stand in these patients. Two inter-related studies were carried out. In the first study, 20 patients with PD and 20 control subjects were instructed to perform sit-to-stand at a natural speed. In the second study, 15 control subjects were instructed to simulate the slower speed of sit-to-stand of the patients identified in the first study. Kinematic and kinetic data were recorded by a PEAK motion analysis system and two force platforms. The results showed that patients with PD generated smaller peak horizontal and vertical velocities during the task. They took a longer time to complete each individual phase as well as the whole movement of sit-to-stand. Patients also produced smaller peak hip flexion and ankle dorsiflexion joint torques and had prolonged time-to-peak torques from sit-to-stand onset. When control subjects simulated the patients' speed of sit-to-stand, there was no difference in all the kinematic and kinetic data between groups. The only exception was that they exhibited a shorter transition time between peak horizontal velocity (flexion phase) and seat-off (extension phase) than the patients. This study demonstrated that the slowness of PD patients during sit-to-stand at a natural speed could be attributed to inadequate peak hip flexion and ankle dorsiflexion torques, a prolonged torque production, as well as a difficulty in switching from the flexion to extension direction during sit-to-stand. As the latter difficulty persisted when the control subjects performed the task at a speed similar to that of the patients, our findings suggest that a fundamental problem of patients with Parkinson's disease could be a switch between movement directions.
authors.affiliation: Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hong Kong, Republic of China.
authors.forename: Margaret K Y
authors.initials: MK
authors.lastname: Mak
authors.forename: Christina W Y
authors.initials: CW
authors.lastname: Hui-Chan
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D018476:Hypokinesia / Q000175:diagnosis* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009460:Neurologic Examination; D009949:Orientation / Q000502:physiology*; D010300:Parkinson Disease / Q000175:diagnosis* / Q000503:physiopathology; D011187:Posture / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology*; D012016:Reference Values; D016474:Weight-Bearing / Q000502:physiology