Physical exercise/training causes changes in the following parameters of circulatory system, such as:
(a) Size of the heart
(b) Heart rate
(c) Stroke volume
(d) Cardiac output
(e) Blood volume
(a) Size of the heart: The blood is supplied to the whole body by heart. The size of heart gets changed as a result of endurance training. Endurance training of more than 12 weeks increases the heart's weight and volume, which further increases the thickness of the left ventricle's wall and chambers' size. Then. contraction ability of the heart also increases.
(b) Heart rate: It is the number of times the heart beats per minute. Heart rate is decreased as a result of exercise and training. This decreasing heart rate trend shows the improvement of your cardiovascular fitness.
(c) Stroke volume: It is the amount of blood pumped by the left or right ventricle of the heart per beat. As a result of endurance training the stroke volume increases. Stroke volume for untrained individual at rest is about 55-75 ml. Whereas stroke volume of trained athletes at rest is 80 - 90 ml. In trained athletes the amount of blood pumped is more in one beat as compared to untrained.
(d) Cardiac output: The cardiac output at rest remains unchanged but at maximum level of exercise it increases considerably. This increase results mainly, from the increase in maximal stroke volume. Maximum cardiac output ranges from 14-20 litres/min. and in trained individuals 25-35 litres/min. or more in highly trained athletes engaged in endurance sports.
(e) Blood volume: Exercise/training results in increase in blood volume which is mainly due to increase in blood plasma volume (liquid portion of blood). The number of red blood cells also increases. Increased blood plasma volume decreases blood thickness that can improve circulation of blood and oxygen availability. Highly trained male athletes may have more than 7 litres of total blood volume as compared to untrained having less than 5.6 litres of total blood volume.
