The Athletic Heart

Cardiac Output Cardiac 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 30-35 l/min while most non athletes can only achieve a maximum cardiac output of approximately 20 l/min.

The following table below shows some typical values for cardiac output at varying levels of activity: Activity Level Heart rate (HR) (beats/min) Stroke Vol (SV) (ml) Cardiac output (l/min) (HR*SV) Rest 72 70 5 Mild 100 110 11 Moderate 120 112 13.4 Heavy (highly trained athletes) 200 130 30

Exercise 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.

These changes are caused by: For example, in a relatively untrained person, HR may increase to 70-170 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 Rate Increased release of adrenaline into the blood increases the Stroke Volume An 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.

Endurance Training Endurance Training can reduce resting heart rates to as low as 30-40 beats per min Like 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.

Comparison 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) Untrained 170 120 20 Trained 195 180 35

Summary – Exercise affects the heart and circulation in the following ways Cardiac muscles thicken and contract more forcefully so cardiac muscle strength increases The left ventricular mass increases – a condition known as cardiac hypertrophy The stroke volume increases The cardiac output increases The maximum heart rate during exercise increases Recovery time ( the time taken for the heart rate to return to resting levels ) decreases The resting heart rate is lower

The End