Cognitive performance will be tested and interpreted compared to norms. Performance on motor and balance tasks will be assessed with the Smart Balance Measurement System and the GAITRite System. Physical fitness will be determined by peak oxygen consumption and aerobic threshold as measured by pulmonary gas exchange during an exercise tolerance test on the treadmill. Structural brain volumes will be determined by magnetic resonance imaging (MRI) and cortical connectivity will be quantified using resting state functional MRI and Diffusion Tensor Imaging (DTI) to evaluate integrity of and changes in white matter tracts in response to exercise. Blood will be collected to quantify the presence of biomarkers (such as VEGF, BDNF and IGF-1) and dopamine transmission. Other self-reported measures of quality of life, fatigue severity, depression and sleep quality would also be collected.