– Myoglobin(MB) is a cytoplasmic protein expressed in myocytes of the heart and skeletal muscle that reversibly binds oxygen. It belongs to the globin family. Functions of myoglobin include oxygen storage and transport, as well as scavenging of NO and reactive oxygen species. MB serves as a reserve supply of oxygen and facilitates the movement of oxygen within muscles. Myoglobin also serves as a sensitive marker for muscle injury resulting from cardiac infarction. Surprisingly, mice in which myoglobin has been removed by gene targeting are able to perform extensive exercise and respond normally to hypoxic challenge.