Distinct Directional Postural Stability Deficits Across Lower Limb Musculoskeletal Disorders

Inclusion Criteria: Inclusion criteria for the lateral ankle sprain group will include participants with a clinically confirmed history of unilateral lateral ankle sprain, who are at least three months post-injury to avoid acute inflammatory effects, and who report residual symptoms such as pain or functional limitation. Participants in the patellofemoral pain syndrome group will have a clinical diagnosis of patellofemoral pain syndrome characterized by anterior or retropatellar knee pain aggravated by functional activities such as stair climbing, squatting, or prolonged sitting, with symptoms persisting for at least three months. Healthy control participants will have no history of lower limb musculoskeletal injury, pain, or functional impairment within the past three months and will be matched to the patient groups based on age and sex. All participants across groups will be able to stand independently without assistive devices and will demonstrate sufficient cognitive ability to understand and follow study instructions Exclusion Criteria: Exclusion criteria for all groups will include a history of lower limb fracture or surgery, neurological or vestibular disorders that may affect balance or postural control, uncorrected visual impairments, systemic inflammatory or rheumatological diseases, and metabolic or neurological conditions known to influence neuromuscular performance. Participants currently engaged in structured balance, proprioceptive, or neuromuscular training programs, as well as those taking medications that may affect balance or postural stability, will also be excluded from the study.