There are many changes that occur with your cardiovascular system in response to exercise. During exercise, your body demands more oxygen and nutrients to be delivered to the muscles, causing an increasing in your breathing and heart rate. The increase in demand from the muscles causes more blood to be pumped out through the heart. This is known as cardiac output.
Cardiac Output
Cardiac output is the product of heart rate and stroke volume. The resting value of the cardiac output is about 5.0 L/min depending on the size of the person. This number increases with exercise intensity to between 20 and 40 L/min. Cardiac output varies from person to person depending on body size and fitness level. The major purpose of the increase in cardiac output is to meet the muscles' increased demands for oxygen, according to Jack H. Wilmore and David L. Costill, authors of Physiology of Sport and Exercise.
Heart Rate
Heart Rate increases as exercise intensity increases, until it reaches a plateau in which the heart rate is optimally meeting the circulation demands for your body based on how hard you are exercising. As your heart rate increases, so does your cardiac output.
Stroke Volume
Stroke volume is the amount of blood ejected from the left ventricle during contraction. It allows the heart to work more efficiently during exercise. Stroke volume increases as the rate of work increases but only up to exercise intensities between 40 to 60 percent of maximal capacity, at which point it plateau's, according to Wilmore and Costill. As you begin to exercise, blood begins to circulate at an increased rate, resulting in more blood moving through your heart, thus increasing the amount of the blood ejected.
Exercise
Cardiac output varies based on different activities, because heart rate and stroke volume do not increase or decrease at the same rate. For example, swimmers see a smaller increase in stroke volume compared to runners or cyclists, according Phil Davies of Sports Fitness Advisor. The supine position prevents the blood from pooling in the lower extremities resulting in a lower maximal stroke volume. Whereas, cyclists have a higher stroke volume than runners and swimmers, because of blood pooling associated with the position of being on the bicycle. However, highly-trained cyclist can overcome this blood pooling which will lower their stroke volume and cardiac output to that of runners.
References
- Sports Fitness Advisor: The Cardiovascular System and Exercise
- "Physiology of Sport and Exercise;" Jack H. Wilmore & David L. Costill; 2004
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