Your body's total volume of blood, equaling 4 to 6 L, passes through your heart every minute during rest. Changes in cardiac output during exercise increase blood cycling rate up to 25 L per minute in active individuals and 35 L per minute in elite athletes, says the American Council on Exercise.
Heart health and exercise performance are regulated by your cardiac output ability. Understanding cardiac output during activity enables informed exercise decisions.
Blood Flow Per Minute
According to the American Council on Exercise, cardiac output is the amount of blood flowing out of your heart per minute. Cardiac output is calculated by multiplying heart rate in beats per minute by stroke volume in mL. Direct measurement of cardiac output requires invasive measurements in a clinical setting. However, the University of Michigan provides an equation for cardio output — Cardiac output = stroke volume × heart rate — that doctors typically use.
Heart Rate and Stroke Volume
Heart rate and stroke volume dictate cardiac output. Heart rate is the number of heart beats occurring per minute while stroke volume is the amount of blood pumped from each ventricle per minute. Your heart is comprised of four chambers called atria or ventricles that pump oxygenated blood to working tissue while sending de-oxygenated blood back to your lungs for more oxygen.
Changes During Exercise
Active muscles require more oxygen than resting muscles. At the onset of exercise your muscles signal your heart to pump faster for increased blood flow. In addition, working muscles increase stroke volume by sending higher amounts of blood volume back towards the lungs for oxygen. Therefore, cardiac output rises during exercise due to increased stroke volume and heart rate. The difference between your resting and active cardiac output is called cardiac reserve.
Adaptations to Exercise
Cardiac output adapts throughout a training program. A 2017 American Diabetes Association study that looked at 53 adolescents with Type 1 diabetes concluded that exercise training improves the cardiac output and exercise capacity by increasing the functions of the left ventricle. Therefore, your heart can maintain a high cardiac output with less effort. Most improvement to cardiac output is contributed to increased stroke volume. Positive adaptations occur in as little as three months of aerobic training.
Enhancing Cardio Output
Enhancing cardiac output allows you to maintain lower heart rates during physical activity. For example, at the start of a program you may have a heart rate of 150 beats per minute while running at a 6 mph pace. After three or more months of training increased cardiac output enables you to sustain the same running intensity at a lower heart rate such as 125 beats per minute.
American Council on Exercise reports that when your fitness level has increased enough to start HIIT or high-intensity interval training, your cardiac efficiency increases by elevating your heart's stroke volume and cardio output at a heart rate that is lower. Please consult a doctor before starting any new training program.
- ACE Fitness: "Steady State Vs. Interval Training: Which One is Best for Your Clients?"
- ACE Fitness: "Exercise, The Athlete’s Heart, and Sudden Cardiac Death"
- University of Michigan: "Cardiac Output"
- American Diabetes Association: "Exercise Training Improves But Does Not Normalize Left Ventricular Systolic and Diastolic Function in Adolescents With Type 1 Diabetes"