Males have significantly higher baseline and post-exercise levels of urinary PGE-MUM∙Cr, serum myoglobin, and serum creatinine than females, and these differences are driven by greater total muscle mass and aerobic capacity rather than sex-specific inflammation.

When a person exercises, their muscles experience stress that breaks down small parts of muscle fibers. This damage releases proteins like myoglobin into the blood and triggers a chemical process that produces a compound called PGE2, which the body quickly turns into a stable waste product called PGE-MUM that gets flushed out in urine. Creatinine also rises because more muscle means more natural breakdown of creatine. People with more muscle and better heart-lung fitness have more muscle tissue to damage and higher metabolic activity, so they release more of these substances than people with less muscle or lower fitness.