The aim of this study is to investigate the effectiveness of inspiratory muscle training (IMT) in increasing respiratory muscle strength in patients with juvenile idiopathic arthritis.

Primary pulmonary involvement is an important aspect that leads to morbidity and mortality in adult patients with rheumatoid arthritis [1,2] but is not as frequent in patients with juvenile idiopathic arthritis (JIA), (prevalence; 4-8%) [3]. However, a body of evidence indicates that respiratory functions are affected in more than 50% of all children with JIA, even in those without radiological involvement [1,2,4]. Previous studies comparing children with JIA to their healthy peers showed that forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), peak flow rate (PEF), and carbon monoxide diffusion capacity (DLCO) are decreased and the maximum inspiratory pressure (PImax) and maximum expiratory pressures (PEmax), which are used to assess respiratory muscle strength, are significantly lower [2,4]. In addition, it has been reported that disease-modifying drugs (DMARDs) and non-steroidal anti-inflammatory drugs (NSAIDs), which are frequently used in the treatment of patients with JIA may cause a decrement in respiratory functions [5]. It has been suggested that the decrease in the pulmonary functions in patients with JIA without radiological involvement of the lung parenchyma or thorax may be caused by the weakness of inspiratory and expiratory muscles [2]. Moreover, symptoms and signs such as chronic joint pain and stiffness, synovitis, and deformity seen in children with JIA may limit movement, leading to an inactive lifestyle. Evidence suggests that children with JIA have lower levels of physical activity than age-matched controls [6,7]. This inactive lifestyle accompanying the disease process; may cause decline in aerobic and anaerobic capacity, peripheral muscle strength and quality of life [8,9].

Inspiratory muscle training (IMT) is defined as a technique that aims to improve the function and strength of respiratory muscles through performing exercises with a specialized device [10,11]. There is evidence that the IMT method improves functional status and increases respiratory muscle strength, respiratory volumes, and aerobic exercise capacity in adult rheumatologic patients [12,13]. IMT seems to increase perfusion and muscle metabolism in both respiratory and extremity muscles, provide muscle fiber type conversion, create neural plasticity at respiratory synapses in the central nervous system, and modulate dyspnea in different populations [14]. Despite this, the effectiveness of IMT has not been investigated in patients with JIA.

Inclusion Criteria:

• Being diagnosed with JIA according to International League of Associations of Rheumatology (ILAR) criteria by a specialist pediatric rheumatologist.
• Being between the ages of 13-18.
• To be able to understand and speak the Turkish language adequately.
• Being on the same biological agent treatment for the last three months.
• Agreeing to participate in the research.
• The patient's family accepts the child's participation in the study.
• Having a history of arthritis in at least one joint in lower extremities.

Exclusion Criteria:

• Presence of a condition that prevents performing respiratory muscle training therapy
• Being involved in a different physiotherapy and rehabilitation program six months before the start of the study
• Having a regular exercise habit during last six months (applying a structured exercise program at least 3 days a week)
• Presence of a different pathology that may affect cardiovascular fitness, pulmonary capacity, walking capacity or quality of life.
• Being diagnosed with systemic JIA clinical subtype.

An independent assessor who is unaware of the group of participants going to perform all evaluations.