The goal of this observational cross-sectional study is to investigate the relationship between functional measures of balance and gait and objective kinetic and kinematic parameters in people with Multiple Sclerosis (MS).

The main questions it aims to answer are:

i) What is the relationship between kinetic and kinematic gait and balance parameters measured using the Vicon motion analysis system and performance on clinical functional assessments in people with Multiple Sclerosis?

ii) Which biomechanical parameters are most strongly associated with functional balance, gait, and physical performance outcomes?

Participants will attend a single laboratory-based assessment session. During this session, they will undergo biomechanical gait and balance analysis using the Vicon motion capture system, complete functional assessments of balance, gait, and physical performance, complete questionnaires assessing fear of falling and fatigue, and undergo assessment of lower-limb spasticity.

Multiple Sclerosis (MS) is a chronic immune-mediated disease of the central nervous system characterized by demyelination and neurodegeneration. Impairments in balance and gait are among the most common manifestations of the disease and are associated with reduced mobility, increased risk of falls, decreased independence, and lower quality of life. Accurate assessment of these impairments is essential for clinical decision-making and the development of effective rehabilitation interventions.

Clinical functional assessments are widely used to evaluate balance, gait, and physical performance in individuals with Multiple Sclerosis. In parallel, advances in motion analysis technology have enabled the objective quantification of movement characteristics through kinetic and kinematic measurements. Although both approaches are commonly used in clinical and research settings, the relationship between objective biomechanical parameters and functional clinical outcomes remains insufficiently understood.

The purpose of this cross-sectional observational study is to investigate the associations between kinetic and kinematic measures of balance and gait obtained through three-dimensional motion analysis using the Vicon system and functional performance outcomes in people with Multiple Sclerosis. By examining these relationships, the study aims to identify biomechanical indicators that are most closely related to functional abilities and mobility limitations.

Participants will undergo a comprehensive laboratory-based assessment including biomechanical analysis of balance and gait, standardized functional performance testing, patient-reported outcome measures related to fear of falling and fatigue, and assessment of lower-limb spasticity. Correlation analyses will be conducted to explore the relationships between biomechanical and functional measures.

The findings of this study may contribute to a better understanding of the biomechanical determinants of functional performance in people with Multiple Sclerosis and support the selection of clinically meaningful assessment tools for rehabilitation practice and future research.

Inclusion Criteria:

• Adults (≥ 18 years) with confirmed diagnosis of Multiple Sclerosis
• Expanded Disability Status Scale (EDSS) score <6
• Ability to ambulate independently without the use of assistive devices
• Absence of significant orthopedic or neurological conditions affecting mobility
• Ability to understand and follow verbal instructions.

Exclusion Criteria:

• History of injury or surgical intervention to the lower limbs or spine within the past year
• Any musculoskeletal, neurological, cardiovascular, or other medical condition, other than Multiple Sclerosis, that may significantly affect gait or balance or compromise participant safety during testing.
• Severe balance impairment or high risk of falling that prevents safe participation in single-leg stance, gait analysis, or obstacle negotiation tasks.

The study population will consist of adults with a confirmed diagnosis of Multiple Sclerosis (MS) who are able to walk independently and safely participate in balance and gait assessment procedures. Participants will be recruited from two patient organizations in Western Greece: the "Friends and Persons with Multiple Sclerosis Association" of Northwestern Greece and the Hellenic Multiple Sclerosis Society of Western Greece.