This is a quasi-experimental pre-post trial aimed at investigating the effects of respiratory muscle training (RMT) as trunk stabilization exercise in patients diagnosed with multiple sclerosis (MS)

Multiple sclerosis (MS) is a chronic disease of the central nervous system that can affect various bodily functions, including the respiratory muscles. Weakness in these muscles can lead to a range of complications, including impacting trunk stability, which may result in difficulties maintaining a balanced and stable posture.

While the impact of MS on respiratory muscles and trunk stability is an area of interest in medical research, a definitive consensus on the efficacy of respiratory muscle training (RMT) to improve trunk stability in MS patients has not yet been reached. Several studies have yielded mixed results, leading to uncertainty regarding the effectiveness of this specific intervention.

The complex nature of multiple sclerosis necessitates a multidisciplinary approach to address its various clinical manifestations. In addition to pharmacological treatment, physical and occupational therapy play a crucial role in symptom management and improving patients' quality of life. Although respiratory muscle training may offer potential benefits, further research and well-designed clinical trials are needed to determine its effectiveness and role in the comprehensive management of trunk stability in MS patients.

- General objective: The aim of this study is to investigate the effects of respiratory muscle training (RMT) as a trunk stabilization exercise in patients diagnosed with multiple sclerosis (MS).

- Specific objectives: To analyze the effects of RMT on lung function measured through spirometric tests.

To evaluate the effect of RMT on respiratory muscle strength using maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP).

To investigate the changes produced by RMT on abdominal and diaphragmatic muscle structures measured through ultrasound.

To analyze the effect of RMT on trunk control measured with the Trunk Impairment Scale (TIS).

To study the effect of RMT on balance assessed with the Berg Balance Scale (BBS).

To investigate the effect of RMT on gait capacity and transfers evaluated through the Timed Up and Go (TUG) test.

- Study design: This is a quasi-experimental pre-post trial. The research will be conducted following the principles outlined in the Helsinki Declaration and the Personal Data Protection and Guarantee of Digital Rights Act. The conception of this project will follow the standard elements defined in the SPIRIT (Standard Protocol Items: Recommendations for Interventional Trials) statement.

- Sample size: Sample size calculation will be based on data obtained from a pilot study involving 20 subjects. Subsequently, G*POWER software will be used to calculate the sample size using data obtained for the main variable expressed through diaphragm thickness to determine the effect size. Throughout the project, a power of 80%, an alpha error of 0.05 (one-tailed), and a 95% confidence interval will be employed.

- Subjects: Subjects will be recruited through a previously signed agreement with the Multiple Sclerosis Patients Association, the European University of Madrid, and Sanitas. Subjects will belong to the Multiple Sclerosis Patients Association, and sessions will be conducted at Sanitas centers in Madrid affiliated with the agreement.

- Inclusion criteria: Age between 18 and 70 years. Confirmed diagnosis of Multiple Sclerosis based on McDonald's criteria, with a disease duration of more than two years (relapsing or progressive).

All multiple sclerosis patients according to the Expanded Disability Status Scale (EDSS) will be included.

Stable medical treatment for at least six months prior to the intervention. Absence of cognitive impairment, with the ability to understand instructions and achieve a score equal to or greater than 24 on the Mini-Mental State Examination.

*All wheelchair-bound and non-wheelchair-bound patients will be included, as both groups may benefit from the intervention due to increased trunk motor control. However, only subjects capable of walking will undergo walking-related variables or tests (up to 6 on the EDSS scale).

- Exclusion criteria: Diagnosis of another neurological disease or musculoskeletal disorder other than MS.

Diagnosis of any cardiovascular, respiratory, or metabolic disease, or other conditions that may interfere with this study.

Exacerbation or hospitalization in the last three months before initiating the assessment protocol, or during the therapeutic intervention process.

Receiving a cycle of steroids, intravenously or orally, six months before the start of the assessment protocol and within the intervention period of the study duration.

- Variables, measurements, and measurement instruments: Pulmonary function: forced vital capacity (FVC), forced expiratory volume in one second (FEV1) will be obtained.

Muscle strength, MIP and MEP variables: maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) will be measured.

Ultrasound measurements: of the diaphragm (ultrasound measurement of diaphragm thickness; ultrasound measurement of diaphragm excursion), of the abdominal musculature (ultrasound measurement of abdominal diastasis and abdominal wall).

Trunk Impairment Scale (TIS): static and dynamic trunk stability will be measured.

Berg Balance Scale (BBS): patient balance will be measured. Timed Up and Go (TUG): activity limitations will be assessed. Therapeutic adherence.

- Therapetic intervention program: Before starting the therapeutic intervention protocol, patients will be informed about the study through an informed consent form (APPENDIX I), which they will sign and submit. The necessary material for conducting the intervention will also be provided, which will be delivered to the patient's home.

The therapeutic intervention program will be carried out for 30 minutes, twice a day, and six times a week, following the protocol by Lee et al.

Note: During respiratory work, patients may experience dizziness, headaches, changes in heart rate, or desaturations. Therefore, to maintain safety margins, participants will be continuously monitored with an FDA-approved fingertip pulse oximeter.

To determine the percentage of work of MIP and MEP, this variable will be taken using a Micro RPM® respiratory pressure device from Micro Medical, Kent, United Kingdom. Participants will work at 40%-60% of the maximum MIP and MEP, according to the clinical trial by Brita Klefbeck et al.

Respiratory muscle training will be performed with the Threshold IMT-Philips inspiratory training device and the Threshold PEP expiratory training device, both from Respironics®. Participants will be comfortably seated in a chair with their feet on the ground, without back support, and with the trunk at a 90° angle to the hips. A conventional nasal clip will be used to prevent air leaks. In forced expiratory training, participants will use the ThresholdPEP® with a custom mouthpiece and perform forced expiration through the resistance device. Inspiratory muscle training will follow the same procedure using the Threshold IMT®.

Both inspiratory and expiratory training will be repeated 10-15 times, 5 sets for 20 minutes in one session, with a rest time of 30-60 seconds between each set.

Patients will receive a phone call every Monday during the 6 weeks of the intervention to check if they are performing the exercises and to answer any questions arising from the training.

- Statistical methods: Qualitative variables will be expressed as absolute number and percentage, and quantitative variables as mean ± standard deviation if they follow a normal distribution, or as median and interquartile range (IQR) if not. Kolmogorov-Smirnov or Shapiro-Wilk tests (if the sample is less than 50) will be used to check the normality of data distributions.

Inclusion Criteria:

• Confirmed diagnosis of Multiple Sclerosis based on McDonald criteria, with a disease duration of more than two years (relapsing or progressive) (McDonald et al., 2001).
• All multiple sclerosis patients are included according to the Kurtzke Disability Status Scale (EDSS) ANEX II (Kurtzke 1983, Tollár 2020).*
• Stable medical treatment for at least the six months prior to the intervention (Tollár, 2020).
• Absence of cognitive impairment, with the ability to understand instructions and achieve a score equal to or greater than 24 on the Mini-Mental State Examination (Folstein, Folstein & McHugh, 1975, Tollár 2020).

Exclusion Criteria:

• Diagnosis of another neurological disease or musculoskeletal alteration other than MS.
• Diagnosis of any cardiovascular, respiratory, or metabolic disease, or other conditions that may interfere with this study.
• Experienced exacerbation or hospitalization within the last 3 months prior to initiating the assessment protocol, nor during the therapeutic intervention process.
• Received a cycle of steroids, intravenously or orally, 6 months prior to the start of the assessment protocol and within the study intervention period.

The study data will remain in a repository and will be available upon request from the plaintiffs.

Blinding will involve the evaluators, who will be unaware of which intervention group each subject belongs to