Additional Study Information: We are studying the relationship between mitochondrial function and the experience of fatigue. Mitochondria are the powerhouses of the cell. Cells within different organs contain hundreds to thousands of mitochondria, which sustain life and fuel energy-dependent processes that we do every day including muscle contraction and cognitive activity. They act like a digestive system, which takes in nutrients, breaks them down, and creates energy rich molecules for the cells to function, and they have been shown to be associated with the experience of fatigue. As part of this study, you will be asked to have two tubes of blood drawn. The purpose of this blood draw is to investigate the relationship between mitochondrial functioning in the body and levels of fatigue experienced by depressed individuals. Some of you may also be asked to undergo magnetic resonance imaging (MRI) exam. The purpose of the MRI exam is to investigate muscle fatigue in depressed individuals.