Inspiratory Muscle Training in Patients With Inflammatory Myopathy

Idiopathic inflammatory myopathies (IIM) are rare autoimmune disorders characterized by progressive, symmetrical proximal muscle weakness, frequently affecting the respiratory muscles. Diaphragmatic dysfunction and reduced inspiratory muscle strength contribute to impaired ventilation, fatigue, and reduced exercise tolerance. While exercise training has proven beneficial in patients with various neuromuscular conditions, evidence regarding inspiratory muscle training (IMT) in IIM is lacking.

This pilot interventional study will prospectively evaluate the impact of a 3-month IMT program on respiratory and functional outcomes in patients with IIM. The intervention consists of daily inspiratory resistance training (30 breaths/day, 7 days/week) using the Threshold IMT device (Philips Respironics, USA). Training intensity is set at 30% of maximal inspiratory pressure (MIP) and adjusted progressively based on patient-reported exertion. Participants receive individualized instruction, follow-up phone consultations every 2 weeks, and record adherence in exercise diaries.

Assessments include inspiratory muscle strength (measured with Powerbreathe KH2), spirometry (Forced Expiratory Volume in 1 Second, Forced Vital Capacity, Forced Inspiratory Vital Capacity, Inspiratory Reserve Volume), diaphragm ultrasound (mobility and thickness fraction), six-minute walk test (6MWT), fatigue assessment (Borg Rating of Perceived Exertion Scale, Fatigue Severity Scale), and quality of life (36-Item Short Form Health Survey). Outcomes will be measured 3 months before training, at baseline, after 3 months of training, and during extended follow-up (up to 6-12 months). The primary endpoint is change in MIP. Secondary endpoints include pulmonary function parameters, diaphragmatic function, exercise tolerance, fatigue, and health-related quality of life.

The study will be conducted in the Neurology Clinic of the Medical University of Warsaw (WUM). A total of 33 patients with IIM, diagnosed according to European Alliance of Associations for Rheumatology / American College of Rheumatology criteria, will be recruited. Inclusion requires age ≥18 and written informed consent. Exclusion criteria include cognitive impairment, acute respiratory infection, prior respiratory training, pneumothorax, pulmonary hypertension, or contraindications to IMT. This trial is expected to provide the first structured evidence on the role of IMT in improving functional status in patients with inflammatory myopathy, potentially guiding individualized rehabilitation strategies for this patient population.

• Inspiratory Muscle Training (IMT) (Behavioral): Inspiratory muscle training performed with a threshold loading device (Threshold IMT, Philips Respironics). Participants perform 30 breaths once daily, 7 days per week, for 3 months. The training load is set at 30% of maximal inspiratory pressure (MIP) and increased by 10% if the perceived exertion decreases on two consecutive training days. Participants receive individualized instruction and regular follow-up consultations (every 2 weeks) to adjust load and verify adherence.

Primary outcomes

• Change in maximal inspiratory pressure (MIP) [3 months before training, baseline, 3 months (end of training), 6 months, 9 months, 12 months]: Maximal inspiratory pressure (MIP) measured at the mouth using Powerbreathe KH2 devices. Results are expressed in cmH₂O. Higher values indicate greater inspiratory muscle strength.

Secondary outcomes

• Change in Forced Vital Capacity (FVC) [3 months before training, baseline, 3 months (end of training), 6 months, 9 months, 12 months]: Forced Vital Capacity (FVC) assessed by spirometry using the EasyOne spirometer (NDD Medical Technologies). Results are expressed in liters (L) and as percent of predicted values (% predicted). Higher values indicate better pulmonary function.
• Change in Forced Expiratory Volume in 1 Second (FEV1) [3 months before training, baseline, 3 months (end of training), 6 months, 9 months, 12 months]: Forced Expiratory Volume in 1 Second (FEV1) assessed by spirometry using the EasyOne spirometer (NDD Medical Technologies). Results are expressed in liters (L) and as percent of predicted values (% predicted). Higher values indicate better pulmonary function.
• Change in diaphragm thickness [3 months before training, baseline, 3 months (end of training), 6 months, 9 months, 12 months]: Diaphragm thickness assessed by ultrasound using a Philips Lumify linear probe. Thickness is measured in millimeters (mm) at end-expiration and end-inspiration. Diaphragm thickening fraction (%) may be calculated from inspiratory and expiratory thickness measurements.
• Change in 6-Minute Walk Distance (6-Minute Walk Test) [3 months before training, baseline, 3 months (end of training), 6 months, 9 months, 12 months]: Functional exercise capacity assessed by the 6-Minute Walk Test (6MWT), conducted on a 30 m corridor. The total distance walked in 6 minutes is recorded in meters. Greater distance indicates better functional exercise capacity.
• Change in perceived exertion (Borg Rating of Perceived Exertion) [3 months before training, baseline, 3 months (end of training), 6 months, 9 months, 12 months]: Perceived exertion assessed using the Borg Rating of Perceived Exertion Scale (modified 0-10 scale). The scale ranges from 0 (no exertion) to 10 (maximal exertion), with higher scores indicating greater perceived exertion and fatigue.
• Change in fatigue severity (Fatigue Severity Scale) [3 months before training, baseline, 3 months (end of training), 6 months, 9 months, 12 months]: Fatigue assessed using the Fatigue Severity Scale (FSS), a 9-item questionnaire in which each item is scored from 1 (strongly disagree) to 7 (strongly agree). The total score is calculated as the mean of the 9 items (range 1-7), with higher scores indicating greater fatigue severity.
• Change in quality of life (36-Item Short Form Health Survey) [3 months before training, baseline, 3 months (end of training), 6 months, 9 months, 12 months]: Health-related quality of life assessed using the 36-Item Short Form Health Survey (SF-36). The questionnaire includes eight domains scored from 0 to 100, with higher scores indicating better health status and quality of life.

Sex: All, ages: 18 Years to any

Inclusion Criteria:

* Diagnosis of inflammatory myopathy according to European Alliance of Associations for Rheumatology / American College of Rheumatology criteria
* Age ≥ 18 years
* Stable clinical condition allowing participation in physical activity
* Ability to understand and follow instructions
* Written informed consent to participate in the study

Exclusion Criteria:

* Cognitive impairment preventing proper exercise performance
* Current respiratory tract infection
* Previous respiratory muscle training within the last 12 months
* History of spontaneous pneumothorax
* Pulmonary hypertension
* Tympanic membrane rupture or other middle ear pathology
* Lack of voluntary and informed consent

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