Control
of heart rate when training is perhaps the most important idea to remember when
trying to excel. If you keep the heart rate too low when training you will find
it difficult to progress further or faster, if you keep the heart rate too high
you will find it impossible to recover or progress to better performances.
Blood
flows from the heart into the arteries, through capillaries (where nutrients
escape and waste is collected), into the veins and back to the heart.
Most
people think of the heart as being a pump. In theory the heart is a pump but
that's not the whole story. If the heart only functioned as a pump then our
vascular system would be a system of hydraulics. But that's not true. Our
vascular system is a system of hydrostatics. A system of hydrostatics means
water (or blood in our case), will flow from an area of high concentration to
an area of low concentration (osmosis).
Our
blood vessels (arteries and veins) have a muscular layer in the walls; these
muscles can contract or relax depending on the needs of the body. This action
causes a sucking motion to the fluid (blood) by a change in hydrostatic
pressure, during this process the heart functions not only as a pump, but also
as a reservoir. In this way we change the diameter of the blood vessels and
therefore, the amount of piping in our bodies, which reduces the demands placed
on the heart. This enables us to be more cost effective, run faster and perhaps
even live longer.
Cardiac
output (the amount of blood leaving the heart) is determined by the amount of
blood returning from the veins (mean systemic filling pressure) and rate/rhythm
of contraction (beats per minuet BPM). Both of these factors can be altered by
exercise and body composition and therefore heart rate can be controlled.
When
we exercise, our muscles require more fuel and oxygen to meet the demands
placed on them. This is achieved by increasing blood supply. Increase blood
supply also removes the resultant waste (lactic acid and CO2), which is
produced as a result of this process. The nervous system relaxes the muscles in
the veins, so the blood to flows through the muscle at a faster rate,
delivering the essential nutrients and removing waste. Wider veins with larger
carrying capacity mean greater return of blood to the heart and therefore
greater pressure in the heart.
Starling’s
law states that the pressure before cardiac contraction governs the force of
cardiac contraction. Since the pressure has gone up with the increase of flow
through the veins, the heart will now contract with more force. Now the
pressure on the arterial side will go up too. This causes the muscular layer in
these vessels to stretch more than at rest.
After
it contracts the heart is at rest. In a system of hydraulics the blood would
stop flowing, but this can’t happen because stagnant blood clots very quickly.
So the muscular layer in the arteries (which have been stretched) start to
contract. This arterial contraction keeps the blood moving although the heart
is momentarily resting, by use of pressure changes (hydrostatics).
Now
the arteries will force more blood though the capillaries into the veins,
increasing the venous return further and therefore the force of cardiac
contraction.
The
body has a set distance of blood vessels. Think of the vessels being like pipe
lines. There are large, medium and small sized pipes. The diameter of these
pipes can be made wider or narrower; this will increase or decrease the
pressure inside them by varying the volume of blood they can hold. The very
small pipes supply the same areas of muscle as neighbouring pipes and as a
consequence we don’t use the majority of them. So we shut them down.
When
we begin running we increase the demand of the muscle cells. Now we need to increase
blood flow. This increase will force some of these small pipes to open. If we
are consistent with running we can maintain these new opened pipelines. As we
run more and more we open more pipelines in order to meet demands. These new
pipes will mean we can supply much more nutrients to the muscle cell and remove
more waste. And now that there are more pipes open it will reduce the overall
pressure in the system. This means venous return will be less, so the filling
pressure in the heart is less which means rate/rhythm of contraction is less.
What
this means to a runner or cyclist is that heart rate will be lower so you can
exercise for longer periods and more quickly. All of this is possible if consistency
in training is maintained. If the demand on these small pipes (capillaries) to
carry blood is not met they will once again shut down. Running or cycling three
times a week ensures that these vital pipelines remain open. The overall drop
in systemic pressure as a result of new pipelines being open means the demands
on the heart is less. This is why an athlete has a low resting heart rate. Most
of the blood is being reserved in the systemic vessels instead of the heart.
Less pressure in the heart means less demand on the coronary arteries and this
reduces the risk of coronary heart disease significantly.
Coronary
heart disease is number one killer in the western world. A person with coronary
heart disease is likely to have angina and is at huge risk of heart attack
(infarct), although this is not the only mechanism for having a heart attack it
is by far the most likely.
When
the heart contracts and the blood is forced out into the arteries, the arteries
stretch in diameter under the pressure produced by the heart contraction. The
highest pressure reached in the arteries is called the "systolic"
pressure. After the hearts contraction the muscle layer in the artery (which is
now under stretch) will begin to contract and squeeze the blood around the
body. This arterial contraction will reduce the pressure in these arteries, the
least pressure will be right before the next heart contraction. This is called
the "diastolic" pressure. Your blood pressure is monitored by these
two readings along with your heart rate. Regular exercise will help to keep
these readings to the norm and will prevent excess pressure on the heart.
I
believe that we need to stop teaching people that the heart is a pump. If we
all understand the importance of blood dynamics in arteries and veins and the
role of exercise, we might be able to reduce the number 1 cause of death in the
western world. Heart Attack!
Neil
www.neiltheosteo.com