How does altitude training potentially benefit an athlete?

Altitude training is beneficial primarily because it increases the number of red blood cells in the body. When an athlete trains at high altitude, the lower oxygen levels stimulate the production of erythropoietin (EPO), a hormone that promotes the formation of red blood cells in the bone marrow. This increase in red blood cells enhances the oxygen-carrying capacity of the blood, allowing athletes to utilize oxygen more efficiently during physical activities.

As a result, athletes who engage in altitude training can improve their aerobic endurance and overall performance at lower altitudes when they return to sea level. This adaptation is crucial because improved oxygen delivery helps in sustaining higher levels of intensity during endurance events, making altitude training a favored strategy among elite athletes.

In contrast to this correct option, the other choices do not accurately reflect the primary benefits of altitude training. Training at high altitude typically does not decrease muscle mass; instead, athletes often focus on endurance and cardiovascular capacity. Additionally, while altitude training can lead to various physiological adaptations, it does not specifically reduce the risk of injury or enhance agility in a direct manner.