Impact of Force Control of Hip Abductor Muscles on Postural Control in Middle-aged and Older Adults and Individuals With Parkinson's Disease

Both aging and Parkinson's disease (PD) negatively affect postural control and increase the risk of falls, with frontal plane balance being particularly challenging for these populations. Previous studies have mainly focused on sagittal plane balance and have identified the important roles of ankle plantar flexors and knee extensors; however, the contribution of hip abductor muscles-key muscles for frontal plane stability-remains unclear, particularly in terms of their force production and control abilities. Therefore, this study aims to investigate hip abductor muscle force production and force control, and to examine whether these factors are associated with postural control, gait, and balance performance in individuals across different ages and those with PD. Healthy young, middle-aged, and older adults will be recruited from the community, and individuals with PD will be recruited from the Department of Neurology. Healthy participants must be in good health, able to walk independently, demonstrate normal cognitive function, and provide informed consent, while those with neurological, cardiovascular, musculoskeletal, or other conditions affecting motor performance will be excluded. For individuals with PD, inclusion criteria will be a clinical diagnosis of idiopathic PD, Hoehn and Yahr stages 1 to 3, stable anti-PD medication use, and the ability to follow instructions and walk at least 10 m. Exclusion criteria will include psychiatric, immune, integumentary, or musculoskeletal disorders, neurological conditions other than PD, lower extremity pain, uncontrolled cardiovascular disease, or inability to provide informed consent. All participants will undergo a one-time assessment, including maximal voluntary isometric contraction, force steadiness, postural control, and gait performance.

Surface electromyography will be used to assess neuromuscular function, postural control will be evaluated using a force plate under multiple standing conditions, and gait parameters will be measured at both comfortable and fast walking speeds. Statistical analyses will be conducted using ANOVA to examine group differences.