Why does Hematocrit tend to decrease with endurance training?

Hematocrit tends to decrease with endurance training primarily due to an increase in plasma volume. As athletes engage in prolonged exercise, their bodies adapt by expanding plasma volume to improve circulation and oxygen delivery to muscles. This dilution effect lowers the concentration of red blood cells relative to the total blood volume, resulting in a decrease in hematocrit. Additionally, endurance training can lead to increased red blood cell turnover and a temporary reduction in red blood cell production.