Multiple sclerosis (MS) is a chronic and progressive autoimmune disease of the central nervous system characterized by inflammation, demyelination, and axonal degeneration. Depending on lesion localization and disease severity, individuals with MS may develop a wide range of neurological manifestations affecting motor and sensory functions.

Current evidence indicates that pulmonary function impairments may occur in individuals with MS even in the absence of overt respiratory symptoms. Compared with healthy individuals, people with MS have been reported to exhibit significantly reduced values in several respiratory parameters, particularly respiratory muscle strength. Moreover, these reductions appear to become more pronounced in parallel with increasing Expanded Disability Status Scale (EDSS) scores, regardless of disease duration. Indeed, previous studies have demonstrated that even individuals with MS who have mild disability levels (EDSS 0-4.5) experience significant declines in respiratory muscle strength, pulmonary function, and functional exercise capacity compared with healthy controls.

These findings suggest that the respiratory system may be affected not only in the advanced stages of MS but also during the early phases of the disease, with functional impairments emerging before clinically evident respiratory complaints arise. Despite this, the existing literature lacks studies that define clear, clinically applicable cut-off values for respiratory muscle strength and endurance that can discriminate disability levels in individuals with MS. This gap highlights the absence of objective criteria that clinicians can rely on for early detection and for planning targeted rehabilitation interventions.

The present study aims to address this gap by identifying optimal cut-off points for respiratory muscle strength and endurance in individuals with MS to facilitate early and accurate discrimination of disability status. By doing so, this research seeks to make an original contribution to the literature. The findings are expected to support the standardization of respiratory assessment processes in clinical practice, thereby improving patient quality of life and enhancing the efficiency of healthcare services. Furthermore, the results will provide a strong scientific basis for integrating respiratory function assessments into MS follow-up protocols and will offer a methodological framework for future intervention-oriented studies.

Inclusion Criteria:

• Diagnosed with multiple sclerosis,
• Aged 18 years or older,
• Able to communicate effectively (able to speak, understand, read, and comprehend Turkish),
• No relapse within the past three months,
• Clinically stable for at least the past one month,
• No participation in respiratory-based rehabilitation programs within the past six months,
• Voluntary participation in the study.

Exclusion Criteria:

• Presence of neurological disorders other than multiple sclerosis,
• Presence of autoimmune diseases other than multiple sclerosis (e.g., rheumatoid arthritis, type 1 diabetes mellitus, systemic lupus erythematosus),
• Presence of chronic cardiac or pulmonary diseases that may affect respiratory muscle strength or pulmonary function, such as chronic obstructive pulmonary disease (COPD), asthma, interstitial lung disease, or heart failure,
• Pregnancy or breastfeeding,
• Inability to comply with the testing procedures.

Adults aged 18 years and older diagnosed with multiple sclerosis who are clinically stable, able to communicate effectively, and eligible for respiratory muscle strength and endurance assessments.