1. The Athletic Heart

2. 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 l/min while most non athletes can only achieve a maximum cardiac output of approximately 20 l/min.

3. 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

4. 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.

5. These 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 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.

6. Endurance Training
Endurance Training can reduce resting heart rates to as low as 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.

7. 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

8. 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

9. The End