Adapting effects in our cardiovascular system for a longer period are:
(i) Cardio output increases: The cadiac 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. For highly endurance trained athletes the cardiac output is 40 l/min, or more.
(ii) Increase in stroke volume: physical exercise, especially endurance training, increases the stroke volume. In trained athletes, who endure for long duration, the left ventricle of heart holds more blood during relaxed state than it does in an untrained athlete‟s heart. It means more blood is available to enter the ventricle, which available ultimately increases stroke volume. It also results in decrese in heart rate at rest.
(iii) Lung volume: With endurance training lung volume and capacities increase. Vital capacity is also increased after long duration workouts.
(iv) Tidal volume increases: the tidal volume is the ampunt of air inspired or expired per breath. It also increases as a result of long hours training. In untrained individual the tidal volume is 500 ml/breath, whereas in trained persons it increases to more than 600- 700 ml/breath.
(v) Blood flow: It is a well-known fact that active muscles require more oxygen and nutrients. To fulfil this requirement,more blood must be supplied to these muscles during exercise. The adaptive effect that takes place is that the muscle becomes better trained and the circulatory system adapts to increased blood flow to them.
