Your cardiovascular system consists of your heart, blood vessels and blood. All of these work together to deliver nutrients and oxygen to, and remove waste from, the cells of your body. Your cardiovascular system is especially crucial during exercise, as oxygen demand and waste production in your active muscles increase. Initial responses of your cardiovascular system work together to allow you to meet the increased demands placed on it with exercise.
Increased Heart Rate
A resting heart rate averages between 60 and 80 beats per minute, but the rate can exceed 100 beats per minute in middle-aged, sedentary individuals. The rate can also be as low as 20 to 40 beats per minute in endurance-trained athletes, according to the book "Physiology of Sport and Exercise." As you begin to exercise, your heart rate increases proportionately to the intensity of exercise. The higher the intensity, the higher your heart rate. In unconditioned individuals, exercise causes a respectively greater increase in heart rate at any sub-maximal work rate compared with that of a better-conditioned individual.
Increased Stroke Volume
The American College of Sports Medicine, or ACSM, defines stroke volume as the amount of blood ejected from your heart with each contraction. As you begin to exercise, the stroke volume of your heart increases with increasing rates of work, but it increases only up to exercise intensities of about 50 percent of your maximal capacity. After this point, stroke volume levels off and your heart rate must pick up the slack to deliver blood to your working muscles.
Increased Cardiac Output
Cardiac output is the product of heart rate and stroke volume. Because both of these functions increase, your overall cardiac output also increases. The purpose of the increase in cardiac output is to meet your muscles' increased demand for oxygen.
Redirection of Blood
As exercise begins, your active skeletal muscles demand an increased blood supply, and your sympathetic nervous system redirects your blood from areas where it is not essential to your working muscles. "Physiology of Sport and Exercise" notes that this is mainly accomplished by reducing blood flow to your kidneys, liver, stomach and intestines. As the exercise causes your body heat to rise, more blood is redirected to your skin to conduct heat away from your body's core.
Increased Systolic Blood Pressure
According to the ACSM, whole-body endurance exercise causes your systolic blood pressure to increase proportionately with exercise intensity. This increase results from your increased cardiac output that also accompanies exercise; the increased blood flow puts more pressure on the walls of your vessels. Increased blood pressure helps drive your blood quickly through your vessels. Regardless of the intensity of your exercise, diastolic blood pressure changes little, if any, during endurance exercise.