What best describes the effects of endurance training at maximal exercise intensity?

Endurance training at maximal exercise intensity leads to increased cardiac output, which is crucial for improving athletic performance and overall cardiovascular fitness. Cardiac output, defined as the amount of blood the heart pumps per minute, is a product of heart rate and stroke volume. With endurance training, the heart becomes more efficient, capable of pumping larger volumes of blood with each beat and often at a lower resting heart rate. This adaptation allows for enhanced oxygen delivery to the muscles, which is vital during high-intensity exercise.

Increased cardiac output supports higher levels of physical exertion by ensuring that working muscles receive the necessary nutrients and oxygen while also helping to remove metabolic waste products more effectively. This improved efficiency not only enhances performance at maximal exercise intensities but also contributes to better performance in endurance activities over time.

Other options, such as lower oxygen extraction, decreased blood flow to muscles, and decreased energy expenditure, do not accurately reflect the physiological adaptations that occur with endurance training. Instead, endurance training promotes greater oxygen extraction by the muscles and improved blood flow, which collectively aid in sustaining performance during high-intensity exercise. Additionally, energy expenditure typically increases with intensity due to higher demands from working muscles rather than decreasing.