The project aims to understand the underlying mechanisms by which physical inactivity causes diseases. This the investigators will study the full spectrum of physical activity, from the most inert of the most active people. The investigators have already collected muscle biopsies and established stem cells from people with Type 2 diabetes, obese healthy and normal weight healthy. In this study, the investigators will establish a cohort of highly physically active marathon runners. In a case-control design, the investigators compare muscle stem cell function across the entire spectrum of physical activity / inactivity.