Final answer:
A cross country runner would have higher glycogen levels in their muscles to provide a quick source of energy during prolonged exercise, enabling efficient production of ATP, which powers muscle activity.
Step-by-step explanation:
The cross country runner would have more glycogen stored in their muscles compared to someone who is not as physically active. Glycogen is the stored form of glucose, which can be quickly mobilized to generate adenosine triphosphate (ATP), the energy currency of the cell, during prolonged or high-intensity exercise.
Through a process known as carbohydrate loading, endurance athletes increase their glycogen stores, enabling them to maintain energy production over long durations. When the body requires a rapid energy source, it breaks down glycogen into glucose, which is then used in cellular respiration to produce ATP. This fueling strategy is advantageous for endurance sports like cross country running, where a steady supply of energy is required.
Moreover, ATP is a more immediate energy source than breaking down carbohydrates directly, because the conversion from glucose to ATP occurs via several biochemical reactions that gradually release energy, making it more metabolically efficient. By contrast, directly using the bonds of carbohydrates for energy would be similar to trying to capture all the energy from a burst of fireworks in one go—it's simply not practical or efficient.