What are the three primary determinants of aerobic exercise efficiency?

The correct choice highlights the three primary determinants of aerobic exercise efficiency as the number of mitochondria, aerobic enzyme concentration, and oxygen-rich blood delivery.

Mitochondria are often referred to as the "powerhouses" of the cell because they are responsible for producing energy through aerobic metabolism. A greater number of mitochondria within muscle cells enhances the muscles' ability to use oxygen for ATP production, directly improving aerobic efficiency.

Aerobic enzyme concentration is critical because these enzymes facilitate the biochemical reactions that convert substrates (like glucose and fatty acids) into usable energy in the presence of oxygen. An increase in enzyme concentration means that these energy-producing processes can occur more rapidly and efficiently.

Lastly, oxygen-rich blood delivery plays a crucial role in aerobic exercise efficiency. The cardiovascular system must effectively transport oxygen from the lungs to the working muscles. Improved blood flow, achieved through a well-conditioned heart and vasculature, ensures that adequate oxygen reaches the muscle tissues during exercise, allowing for better endurance and performance.

These factors combined illustrate how the body's ability to produce and utilize energy aerobically can significantly impact performance outcomes in endurance activities.