RecruitingPhase 1Diagnostic testApplying pGz in Mitochondrial DiseaseThis is a multi-aim study, studying the effects of conventional exercise (measured through Cardiopulomary Exercises Testing or an in-bed pedal exercise) and passive exercise through periodic acceleration (pGz). Aim 1 will focus on the differences between primary mitochondrial disease (PMD) patients and healthy volunteers. Aim 2 is an exploratory aim, which will be studying the effects in patients admitted to the Children's Hospital of Philadelphia Pediatric Intensive Care Unit (PICU).