Inclusion Criteria:  Male subjects at least 10 years of age at time of consent who are willing and able to provide informed consent to participate in the trial and diagnosed with DMD as confirmed by the Investigator Genetically confirmed DMD Reduced ability to walk/run (if ambulatory) Treatment with systemic glucocorticoids for at least 12 months and at a stable dose at least 6 months prior to study participation, except for weight-based or toxicity-related adjustments Current and up-to-date immunizations  Exclusion Criteria:  Left ventricular ejection fraction (LVEF) < 35% Elbow-flexion contractures > 30° in both extremities Body mass index (BMI) > 45 Percent predicted forced vital capacity (FVC%) < 35%