Why do long distance runners have more mitochondria and produce more ATP than people who do not exercise?

Long-distance runners have more mitochondria because their training stimulates the body to adapt to increased energy demands. Mitochondria are the powerhouses of cells, responsible for producing ATP through aerobic respiration. As runners engage in prolonged exercise, their muscles require more energy, prompting an increase in mitochondrial density to enhance ATP production. This adaptation improves endurance and overall performance compared to sedentary individuals.