Abstract
Underlying somatosensory processing deficits of joint rotation velocities may cause patients with Parkinson’s disease (PD) to be more unstable for fast rather than slow balance perturbations. Such deficits could lead to reduced proprioceptive amplitude feedback triggered by perturbations, and thereby to smaller or delayed stabilizing postural responses. For this reason, we investigated whether support surface perturbation velocity affects balance reactions in PD patients. We examined postural responses of seven PD patients (OFF medication) and eight age-matched controls following backward rotations of a support-surface platform. Rotations occurred at three different speeds: fast (60 deg/s), medium (30 deg/s) or slow (3.8 deg/s), presented in random order. Each subject completed the protocol under eyes open and closed conditions. Full body kinematics, ankle torques and the number of near-falls were recorded. Patients were significantly more unstable than controls following fast perturbations (26% larger displacements of the body’s centre of mass; P<0.01), but not following slow perturbations. Also, more near-falls occurred in patients for fast rotations. Balance correcting ankle torques were weaker for patients than controls on the most affected side, but were stronger than controls for the least affected side. These differences were present both with eyes open and eyes closed (P<0.01). Fast support surface rotations caused greater instability and discriminated Parkinson patients better from controls than slow rotations. Although ankle torques on the most affected side were weaker, patients partially compensated for this by generating larger than normal stabilizing torques about the ankle joint on the least affected side. Without this compensation, instability may have been greater.
Highlights
Parkinson’s disease (PD), in the early stages, is characterized by unilaterally occurring symptoms, such as resting tremor and bradykinesia
Slow perturbations may cause instability because 40% of PD patients experience spontaneous movement sensations despite having a normal neurological examination [14]. It is an open question which velocity of support surface movements during stance leads to a better diagnosis of impaired balance control in PD patients
By testing whether support surface perturbation velocity affects postural control in PD patients with respect to healthy controls
Summary
Parkinson’s disease (PD), in the early stages, is characterized by unilaterally occurring symptoms, such as resting tremor and bradykinesia. Slow perturbations may cause instability because 40% of PD patients experience spontaneous movement sensations despite having a normal neurological examination [14] It is an open question which velocity of support surface movements during stance leads to a better diagnosis of impaired balance control in PD patients. We hypothesized that differences in postural control between patients and controls, as expressed by displacement of the body’s centre of mass following support surface movements, would be greater during fast perturbations, due to processing difficulties with proprioceptive inputs that are normally needed to generate correcting forces to keep the body upright. We hypothesized that any observed differences would be more pronounced when visual feedback was lacking
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