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
100
120
70
110
112
5
11
13.4
200
130
30
Mild
Moderate
Heavy
(highly
trained
athletes)
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.
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