Final answer:
Increased heart rate and breathing during aerobic conditioning are caused by enhanced oxygen consumption by muscles. The body's need to supply more oxygen and remove carbon dioxide from the working muscles results in increased respiration and blood circulation.
Step-by-step explanation:
Increased heart rate and breathing during aerobic conditioning are typically caused by enhanced oxygen consumption by muscles. As muscles work harder, they require more oxygen to generate ATP, which is the energy currency of cells. This increased demand for oxygen results in the heart pumping blood faster (increasing heart rate) and the lungs working more efficiently to oxygenate the blood (increasing breathing rate).
In the context of the options you have provided:
- Increased blood pressure is a result of the heart working harder, not a cause of increased heart rate and breathing.
- Decreased lung capacity would not cause an increase in these rates but would rather limit them.
- Reduced cardiac output would decrease the amount of blood being circulated, which is opposite to what happens during aerobic conditioning.
Intense muscle activity leads to an oxygen debt, and the body works to meet this demand with increased respiration and blood flow. This is why we experience increased breathing and heart rate not only during exercise but also for a period afterward as the body returns to its resting state.