National Physical Therapy Examination (NPTE) Practice Exam

What effect does an increase in an athlete's heart rate have when running on a treadmill?

1. A decrease in stroke volume

2. A decrease in cardiac output

3. An increase in stroke volume

4. An increase in cardiac output

The correct answer is: An increase in cardiac output

When an athlete's heart rate increases while running on a treadmill, the body's demand for oxygen and nutrients also rises to support the elevated physical activity. In response, cardiac output, which is the amount of blood the heart pumps per minute, increases. This is achieved primarily through two mechanisms: an increase in heart rate and, to some extent, an increase in stroke volume, which is the amount of blood pumped with each heartbeat. During exercise, as the heart rate rises, the heart needs to pump more blood to meet the demands of the muscles. Consequently, the combination of higher heart rate and potentially increased stroke volume leads to a significant boost in cardiac output. This adaptation enables the body to deliver more oxygen to working tissues, thus supporting sustained physical performance and enhancing endurance. Understanding this relationship is crucial in exercise physiology, as it illustrates how the cardiovascular system responds to increased activity levels. While stroke volume can also increase with training or at lower intensities, during high-intensity exercise like running, the primary mechanism for increasing cardiac output is typically the elevation in heart rate.