Final answer:
During aerobic exercise, heart rate increases to meet the body's increased demand for oxygen and nutrients. This increase in heart rate initially leads to an increase in cardiac output, but at very high heart rates, cardiac output eventually decreases due to decreased stroke volume.
Step-by-step explanation:
During aerobic exercise, heart rate increases to meet the increased demand for oxygen and nutrients in the body. As heart rate increases, the time for the ventricles to fill with blood decreases, leading to a decrease in stroke volume. Initially, cardiac output increases as heart rate compensates for the decrease in stroke volume. However, at very high heart rates, cardiac output eventually decreases as stroke volume decreases further.
The relationship between heart rate and cardiac output is related to the Fick Equation, which states that cardiac output is equal to the product of heart rate and stroke volume. As heart rate increases, cardiac output initially increases due to the compensation from heart rate for the decrease in stroke volume. However, beyond a certain point, the decrease in stroke volume outweighs the increase in heart rate, causing cardiac output to decrease.