Background: Akinesia in basal ganglia disorders is essentially defined by delayed movement initiation; the reaction time increases and it becomes difficult (or even impossible) for the subject to initiate movement. A biomechanical study of gait initiation would help evaluate the role of akinesia in early stage Huntington's disease (HD) patients.
Methods: We recorded kinematic, spatiotemporal and angular parameters (using video motion analysis, a force platform and an optoelectronic system) for the first two steps taken by 15 HD patients and 15 gender- and age-matched controls. In order to evaluate the influence of an external cue on gait initiation parameters, we studied two movement paradigms: self-triggered initiation and initiation triggered (cued) by a "beep" sound. We analyzed kinematic, spatiotemporal (the speed, length and duration of the two first steps) and angular parameters (range of joint angles) as well as kinetic data (the trajectory of the centre of pressure (COP); the speed and trajectory of the centre of mass (COM)).
Results: HD patients presented akinesia in both externally triggered and self-triggered conditions. Patients had more difficulties with self-triggered gait than with triggered gait. In HD, anticipatory postural adjustments (APAs) were more impaired in self-triggered gait initiation than in cued initiation. Indeed, an alteration in the kinetic parameters revealed a reduction in first step speed in both conditions. Hypokinesia (as assessed by a reduction in the range of angle joints) played an important role in this reduction.
Conclusion: Akinesia is a major feature of impaired gait initiation in HD. The deficiencies in self-triggered initiation in HD seen here fit with a hypothesis whereby deficient internal cueing can be replaced by an external trigger.