What is a peptide hormone, specifically EPO known for?

Erythropoietin (EPO) is a peptide hormone primarily produced by the kidneys, and it is known for its crucial role in the regulation of red blood cell production. Specifically, it stimulates the bone marrow to increase the production of red blood cells in response to low oxygen levels in the blood. This process is vital for transporting oxygen efficiently throughout the body, which is particularly beneficial for endurance athletes who require increased oxygen delivery during prolonged physical activity.

While muscle recovery, mental alertness, and bone strength are important aspects of physical performance, they are not directly influenced by EPO in the same way that red blood cell production is. EPO's specific action on red blood cells is what makes it a critical hormone in contexts such as altitude adaptation and athletic performance.