2Cardiac OutputCardiac output varies between each individual and depends on physical fitness and level of activity.For example, the heart of a highly trained athlete can pump l/min while most non athletes can only achieve a maximum cardiac output of approximately 20 l/min.
3The following table below shows some typical values for cardiac output at varying levels of activity:ActivityLevelHeart rate(HR) (beats/min)Stroke Vol (SV)(ml)Cardiac output (l/min) (HR*SV)Rest72705Mild10011011Moderate12011213.4Heavy (highly trained athletes)20013030
4Exercise and the cardiovascular System Cardiac output is increased by increasing both the heart rate and stroke volume, both which increase in proportion to the intensity of exercise.
5These changes are caused by: For example, in a relatively untrained person, HR may increase to beats per min and SV from 70 ml to 120 ml per beat.These changes are caused by:An increased output of sympathetic nerves to the heart which increases the Heart RateIncreased release of adrenaline into the blood increases the Stroke VolumeAn increase in blood volume returning to the heart, increases the rate of filling the heart chambers. This stretches the ventricular walls which respond by contracting more forcibly so that more blood is ejected with each contraction. In other words… the stroke volume is increased.
6Endurance TrainingEndurance Training can reduce resting heart rates to as low as beats per minLike skeletal muscle, cardiac muscle is strengthened by training and is capable of more forceful contraction which increases the stroke volume and as a result the heart of an endurance athlete has a considerably larger SV at rest and during exercise than an untrained individual of the same age.
7Comparison of Maximal CO in Trained and Untrained Individuals When comparing the Cardiac Output during maximal exercise in trained and untrained individuals, it can be seen that the endurance athlete achieves a larger CO mainly because of a relatively greater increase in stroke volume.HR (per min)SV (ml)CO (l/min)Untrained17012020Trained19518035
8Summary – Exercise affects the heart and circulation in the following ways Cardiac muscles thicken and contract more forcefully so cardiac muscle strengthincreasesThe left ventricular mass increases – a condition known as cardiac hypertrophyThe stroke volume increasesThe cardiac output increasesThe maximum heart rate during exercise increasesRecovery time ( the time taken for the heart rate to return to resting levels ) decreasesThe resting heart rate is lower