Use arrows and key terms such as "red blood cells," "oxygen," and "EPO" to describe how high-altitude training helps athletes improve their performance at lower altitudes.

Due to increase red blood cells.

Explanation:

High-altitude training helps athletes to improve their performance at lower altitude because high altitude increases the concentration of red blood cells in the blood. Due to training on high-altitude, the concentration of red blood cell increases in the blood which also increases the consumption of oxygen so when the athletes perform at lower altitude, the more amount of red blood cells in the blood provides natural boost to the muscle due to consumption of more oxygen by the muscle cells.