Exploratory Outcome Measures: MRI changes in muscle architecture and water diffusivity will be assessed by Diffusion EPI MRI. If well tolerated, then we will use a portable device (Ankle IntelliStretch device, RehabTek) to study the effects of exercise on selected MRI measures in leg muscles. Muscle ultrasound will be used to monitor changes in skeletal muscle volume, echogenicity and stiffness. Dynamic breathing MRI will be performed to measure diaphragm motion during free breathing and voluntary maximal inspiration and exhalation.