Stacking Exercises Aid the Decline in FVC and Sick Time

Inclusion Criteria: * Age 6-16 years - This age range was selected as there are accepted normative pulmonary function data and children 6 years of age and older are generally able to reliably perform pulmonary function tests. Children are followed in participating centres until they reach 18 years of age (allowing two years of follow-up). * Clinical phenotypic features consistent with DMD and confirmed by either: (1) Muscle biopsy showing complete dystrophin deficiency; (2) Genetic test positive for deletion or duplication in the dystrophin gene resulting in an 'out-of-frame' mutation; or (3) Dystrophin gene sequencing showing a mutation associated with DMD. * FVC ≥ 30% predicted - This range of pulmonary function was selected to exclude those with severe restrictive respiratory impairment, who are less likely to be able to reliably perform pulmonary function testing over a two year period. * A caregiver willing to provide the therapy * Fluency in English or French Exclusion Criteria: * Unable to perform pulmonary function tests and/or LVR manoeuvre * Presence of an endotracheal or tracheostomy tube * Already using LVR and/or the Respironics in-exsufflator between and during respiratory infections * Known susceptibility to pneumothorax or pneumomediastinum * Uncontrolled asthma or other obstructive lung disease * Symptomatic cardiomyopathy (ejection fraction less than 50% )