SYSTEMATIC REVIEW The Effect of Inspiratory Muscle Training on Duchenne Muscular Dystrophy: A Meta-analysis Elizabeth Williamson, PT, PhD; Natalie Pederson, PT, DPT; Hannah Rawson, PT, DPT; Todd Daniel, PhD Department of Physical Therapy (Dr Williamson), Missouri State University, Springfeld, Missouri; St Luke’s East Outpatient Rehabilitation (Dr Pederson), Lee Summit, Missouri; Kansas City Orthopedic Institute (Dr Rawson), Kansas City, Missouri; Research by Design, LLC (Dr Daniel), Springfeld, Missouri. Purpose: This study reports the respiratory muscle training effect on strength and endurance in individuals with Duchenne muscular dystrophy. Methods: Articles published from 1984 to 2017 were reviewed. Six articles met the inclusion criteria that included within-subject control or between-subject control group, participants with a diagnosis of only Duchenne muscular dystrophy, participation in respiratory muscle training intervention, and outcome measures of endurance and strength. Effect sizes were calculated for each study and overall, weighted mean effect sizes for strength and endurance outcome measures. Results: There was a large effect for improving respiratory endurance and a moderate effect for muscle strength. However, these effects were not signifcant. Conclusion: Findings justify further exploration of the potential benefts of respiratory muscle training for individuals with Duchenne muscular dystrophy. (Pediatr Phys Ther 2019;31:323–330) Key words: Duchenne muscular dystrophy, muscular dystrophy, respiratory muscle training Duchenne muscular dystrophy (DMD) is a progressive dis- order in which initial weakness of large proximal muscles of the shoulder and hip girdles results in an unsteady, waddling gait by age 3 to 5 years, diffculty ascending and descending stairs and rising from the foor by age 5 to 7 years, and loss of the ability to safely ambulate by age 7 to 12 years. 1 Eventually, deformities of the thoracic spine and ribs and weakness of the diaphragm and accessory respiratory muscles compromise pul- monary function. Total lung capacity and vital capacity decrease, and residual volume increases. Effort-dependent components of respiration are affected such as peak expiration fow and forced inspiratory fow. 1 Late in the disease progression, individuals develop cardiomyopathy, which may affect left ventricular con- 0898-5669/110/3104-0323 Pediatric Physical Therapy Copyright © 2019 Academy of Pediatric Physical Therapy of the American Physical Therapy Association Correspondence: Elizabeth Williamson, PT, PhD, Department of Physical Therapy, Missouri State University, 901 S. National Ave, Springfeld, MO 65802 (ewilliamson@missouristate.edu). Natalie Pederson and Hannah Rawson completed the initial work as stu- dents in the Department of Physical Therapy at Missouri State University, Springfeld, Missouri. Supplemental digital content is available for this article. Direct URL citation appears in the printed text and is provided in the HTML and PDF versions of this article on the journal’s Web site (www.pedpt.com) The authors declare no conficts of interest. DOI: 10.1097/PEP.0000000000000648 tractility and right ventricular function. For the majority of indi- viduals with DMD, death occurs following a respiratory infec- tion in early adulthood. 1 The estimated prevalence of DMD ranges from 1.7 to 4.2 individuals per 100 000 in the population. 2 DMD is a genetic disorder in which deletions on the X chromosome prevents the production of dystrophin and related proteins, the dystrophin- glycoprotein complex (DGC). 3 The DGC, a complex of trans- membrane proteins, is associated with the inner surface of the sarcolemma. Dystrophin and dystrophin-associate proteins con- tribute to the maintenance of fber integrity and enable interac- tion of the DGC with microtubulars, actin, and the intermediate cytoskeleton essential for maintenance and repair. 4 Dystrophin is also expressed in cardiac muscle, the neuromuscular junction, the brain, and the retina. 3,4 Without dystrophin, dystrophin-associated proteins are reduced, which disrupts the linkage between the inner surface of the sarcolemma and the extracellular matrix during contrac- tion and relaxation of the muscle. The cascade that follows includes mechanical weakening of the sarcolemma, inappro- priate calcium infux, abnormal signaling, increased oxidative stress, recurrent ischemia, and eventually cell death. 5 Early in the disease, necrotic cells are replaced by proliferation and dif- ferentiation of satellite cells. However, chronic degeneration and impaired regeneration of affected myofbers over time reduce satellite cell capacity and skeletal myofbers are replaced with noncontractile, fbrotic tissue. 6,7 A similar cascade occurs with cardiac muscle. Cardiac myocytes show increased fragility to physiological stretch with associated fbrosis, infammation, and elevation of serum cardiac Copyright © 2019 Academy of Pediatric Physical Therapy of the American Physical Therapy Association. Unauthorized reproduction of this article is prohibited. Pediatric Physical Therapy The Effect of Inspiratory Muscle Training on Duchenne Muscular Dystrophy 323