Myoglobin is an oxygen-binding protein found in skeletal and cardiac muscle cells, where it stores oxygen for use during muscular contraction. When muscle cells are injured, myoglobin is rapidly released into the bloodstream — it is one of the earliest biomarkers to rise after muscle damage.

Myoglobin rises within 1–3 hours of muscle injury, peaks at 8–12 hours, and returns to normal within 24 hours — making it a sensitive early marker of muscle damage. In the context of rhabdomyolysis (severe muscle breakdown), myoglobin levels can become extremely high and cause acute kidney injury when it is filtered and deposits in kidney tubules. Myoglobin is also used as a non-specific early marker of myocardial infarction, though troponin is preferred for cardiac-specific diagnosis.