The
Cardiovascular System and Exercise
The
cardiovascular system serves five important
functions during exercise:
-
Delivers oxygen to working muscles
-
Oxygenates blood by returning it to the lungs
-
Transports heat (a by-product of activity) from the core
to the skin
-
Delivers nutrients and fuel to active tissues
-
Transports hormones
During exercise the working muscles demand more
oxygen and more nutrients. Metabolic process speed
up. More waste products are produced increasing
acidity. Body temperature rises. Combined this leads
to an increase demand on the Cardiovascular system.
Let's take a closer look at some of the immediate
responses your body makes when you begin to exercise
vigorously.
Immediate Response
of the Cardiovascular System to Exercise
Heart Rate
Before exercise even begins heart rate increases in
anticipation. This is known as the anticipatory
response.
After that heart rate increases in direct proportion
to exercise intensity until maximum heart rate is
reached.
Maximum heart rate is estimated with the
formula 220-age. But this is only an
estimation, and not always accurate. The
only direct method for determining maximum heart
rate is to have some exercise at increasing
intensities until a plateau in heart rate is found.
Stroke Volume
This is simply the amount of blood (mL) ejected per
beat from left ventricle.
Stroke volume increases proportionally with exercise
intensity. At rest it averages 50-80mL per beat
increasing up to 100-120ml per beat during intense,
physical activity. What causes the increase?
The
left ventricle fills more completely, stretching it
further and the elastic recoil produces a more
forceful contraction - hence a greater output of
blood.
Cardiac Output
This is the amount of blood (mL) pumped by the heart
in 1 minute. It is a product of stroke volume
multiplied by heart rate. If either heart rate or
stroke volume increase (or both) cardiac output
increase.
Cardiac output increases proportionally with
exercise intensity - which makes sense when you
think both stoke volume and heart rate increase
during activity.
To
give you an idea of how much harder the heart works,
it pumps about 5L of blood per minute at rest and up
to 20-40L per minute during exercise.
Blood Flow
At rest 15-20% of circulating blood supplies
skeletal muscle. During vigorous exercise this
increases to 80-85%.
Blood is shunted away from major organs such as the
kidneys, liver, stomach and intestines. It is then
redirected to the skin to promote heat loss.
Blood Pressure
At rest, a typical blood pressure might read 120/75
mm Hg.
During exercise systolic pressure (the pressure
during contraction of the heart or systole) can
increase to over 200 mm Hg. Diastolic pressure on
the other hand remains relatively unchanged. In
fact an increase of more than 15 mm Hg as exercise
intensity increases can indicate coronary heart
disease.
Adaptations in the
Cardiovascular System
Following an exercise program (of at least 6 weeks,
3x per week) the cardiovascular system and its
components go through various adaptations. Here are
the most important...
Heart Size - weight and volume of the
myocardium (heart) increases.
Heart rate – decreases at rest and during
sub maximal exercise. Time it takes for heart rate to
return to resting levels decreases.
Stoke volume – increases at rest and during
sub maximal exercise.
Left ventricles fill more
completely, producing a more forceful contraction.
<>- during each contraction not all the blood in the
left ventricles is ejected. The percentage that is
pumped is called the ejection fraction and it can
improve following aerobic training.
Blood pressure – can decrease (both systolic
and diastolic pressure) at rest and during
sub maximal exercise by as much as 10 mm Hg.
Blood Flow – greater capillarization in
muscles, improved dilation of capillaries. Possibly
increased collateral circulation to the myocardium
(This is a process in which small, normally closed,
arteries open up and connect two larger arteries or
different parts of the same artery. They can serve
as alternate routes of blood supply).
Blood Volume – significant increase due to
increase in plasma volume and erythrocytes (red
blood cells). This is the main reason why the heart
fills more completely thus increasing stroke volume.
Diagram of the
Heart
Course Contributor Phil Davies
