Myoglobin is an iron-containing pigment present in skeletal muscles. In contrast hemoglobin (4 mol of O2) a myoglobin bind to the single mol of oxygen.
Myoglobin has a higher affinity to oxygen than hemoglobin. In comparison to the hemoglobin oxygen dissociation curve, myoglobin dissociation curve is more leftward. This has the advantage of the transfer of oxygen from the blood to myoglobin in tissues.
O2 from myoglobin released when PO2 is low i.e during exercise. The myoglobin content is greatest in muscles specialized for sustained contraction. The muscle blood supply is compressed during such contractions, and myoglobin can continue to provide O2 under reduced blood flow and/or reduced PO2 in the blood.