The purpose of this research study is to determine the potential of magnetic resonance imaging, spectroscopy, and whole body imaging to monitor disease progression and to serve as an objective outcome measure for clinical trials in Muscular Dystrophy (MD). The investigators will compare the muscles of ambulatory or non-ambulatory boys/men with DMD with muscles of healthy individuals of the same age and monitor disease progression in those with DMD over a 5-10 year period. The amount of muscle damage and fat that the investigators measure will also be related to performance in daily activities, such as walking and the loss of muscle strength. In a small group of subjects the investigators will also assess the effect of corticosteroid drugs on the muscle measurements. Additionally, the investigators will map the progression of Becker MD following adults with this rare disease. The primary objective is to conduct a multi-centered study to validate the potential of non-invasive magnetic resonance imaging and magnetic resonance spectroscopy to monitor disease progression and to serve as a noninvasive surrogate outcome measure for clinical trials in DMD and BMD. The secondary objective is to characterize the progressive involvement of the lower extremity, upper extremity, trunk/respiratory muscles in boys/men with DMD and BMD guiding clinical trials.