Final answer:
High-altitude training can improve performance by increasing hemoglobin levels. Leaving 12 days before the race allows for sufficient acclimation to the altitude.
Step-by-step explanation:
High-altitude training is important for athletes because it can improve their performance in low-altitude races. When training at high altitudes, where the oxygen concentration is lower, the body adapts by producing more hemoglobin, which helps carry oxygen to the muscles. This increase in hemoglobin can provide a performance advantage when the athlete competes at lower altitudes. Leaving 12 days before the race allows the athlete's body to adjust to the change in altitude. It takes about 10 days for the body to re-adjust the hemoglobin level in the blood. By giving themselves 12 days to acclimate, athletes can maximize the benefits of high-altitude training and ensure they are physically prepared for the race.