Multi-muscle synergies in preparation for gait initiation in Parkinson's disease

Objective: We investigated changes in indices of muscle synergies prior to gait initiation and the effects of gaze shift in patients with Parkinson's disease (PD). A long-term objective of the study is to develop a method for quantitative assessment of gait-initiation problems in PD.Methods: PD patients without clinical signs of postural instability and two control groups (age-matched and young) performed a gait initiation task in a self-paced manner, with and without a quick prior gaze shift produced by turning the head. Muscle groups with parallel scaling of activation levels (muscle modes) were identified as factors in the muscle activation space. Synergy index stabilizing center of pres -sure trajectory in the anterior-posterior and medio-lateral directions (indices of stability) was quantified in the muscle mode space. A drop in the synergy index in preparation to gait initiation (anticipatory syn-ergy adjustment, ASA) was quantified.Results: Compared to the control groups, PD patients showed significantly smaller synergy indices and ASA for both directions of the center of pressure shift. Both PD and age-matched controls, but not younger controls, showed detrimental effects of the prior gaze shift on the ASA indices.Conclusions: PD patients without clinically significant posture or gait disorders show impaired stability of the center of pressure and its diminished adjustment during gait initiation.Significance: The indices of stability and ASA may be useful to monitor pre-clinical gait disorders, and lower ASA may be relevant to emergence of freezing of gait in PD. & COPY; 2023 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.

Automated summary

The aim of this study was to investigate changes in muscle synergies prior to gait initiation and the effects of gaze shift in Parkinson's disease (PD) patients. The study found that PD patients showed impaired stability of the center of pressure and decreased adjustment during gait initiation compared to the control groups. The stability indices and anticipatory synergy adjustment (ASA) may be useful for monitoring pre-clinical gait disorders and the emergence of freezing of gait in PD.