What are the effects training on
Heart Rate?
What happens to our bodies as we train and become
more fit?
Sounds
like a simple question right? The
truth is you could write not just an entire book on the subject, but an
entire library of books. I
will address a small portion of that issue here.
I intend to add to the information presented here as I have the
time to write the articles. I
will start out with the issue of heart rate response to a given
workload.
As we
train, out heart becomes a more powerful pump and can do a much better job
of getting blood to the working muscles.
The amount of blood that the heart can pump in a given time period
is known as cardiac output (CO). Cardiac
output is made up of two components: Stroke volume (SV) and heart rate
(HR). Stroke volume is the
amount of blood that the heart pumps each time it beats, and heart rate is
the number of time it beats in a minute. The relationship between cardiac
output, stroke volume, and heart rate can be expressed as:
CO
= SV X HR.
You can see that as either SV or HR increase, so does
CO. Why does this matter? Any
cyclist has observed that as you increase workload, you heart rate goes up
in response. Remember as
heart rate goes up, cardiac output goes up as well.
This increase in cardiac output is required to: deliver more oxygen
and nutrients to the working muscles,
as well as carry away
the CO2, lactate, and other products produced by the working muscles. This is why more work requires greater cardiac output.
As you train, two primary things happen that increase
your stroke volume and therefore allow you to have a decreased heart rate
with the same cardiac output.
One of the adaptations is that your heart rate simply becomes a
stronger muscle. A stronger
muscle can contract more forcefully and force out more blood with each
contraction. Another
adaptation that leads to increased stroke volume is that when you train,
the volume of your blood increases. This increase in blood volume actually
allows more blood to be returned to the heart.
As more blood is returned to the heart, the heart chambers actually
stretch before they contract and push out all of the blood.*
This leads to an even stronger contraction that again increases
stroke volume, and therefore increases cardiac output.
This is why resting heart rate tends to be lower in
trained athletes. These
athletes have very strong hearts that pump more blood with each beat. Resting cardiac output for an individual would be
somewhere around 5
liters/min. If an
untrained person has a resting cardiac output of 70ml per stroke, then
their resting heart rate would need to be about 71 BPM.
This calculation is shown below.
(CO) 5000 ML
= (SV)70ML
X (HR) 71.4 BPM
Now if this individual starts an exercise program,
then SV may easily increase by 20% to 84 ml/min.
Since the cardiac output required at rest does not change with
training, increased SV means heart rate will down down by 12 beats per
minute.
(CO) 5000 ML
= (SV)84ML
X (HR) 59 BPM
This increased stroke volume is why you hear about guys like Miguel Indurain,
Lance Armstrong and Jan Ulrich having resting heart rates that are
down in the 20s or 30s, while your average Joe seldom has a resting heart
rate below 50 BPM. Those
legendary athletes just have very powerful hearts!
This decreased heart rate
not only at rest, but at all workloads as well.
Below is a HR graph of
one of my athletes. I did a
fitness test on him when he first started working with me, and then again
4 months later. The test
protocol involved ramping up the power in the exact same manner on both
occasions. You can see that
in the second test, his heart rate was lower
all power levels.
The advantages of having a decreased HR at a given
power output are obvious. Your
Rate of Perceived Exertion
will be lower given the same intensity (measured in watts or speed), and
you will be able to hold a given power output for a longer period of time.
This shift in the Power/Heartrate curve is only one
of the many adaptations that occur during training.
I hope you find this information useful or interesting.
Feel free to email
me if you have any questions.
Q: When
my training partner and I are riding side by side at the same speed and
neither one of us is drafting, his heart rate is always about 15 beats
lower than mine. Does that
mean he is more fit? Can
I compare my heart rate to his?
A: You cannot compare your heart rate to that of
another rider. As you become
more fit your HR will be lower for the same workload, but you simply
can’t compare two riders.
Q: My
max HR seems to be about 185 beats per minute.
Several of my friends claim that the get their heart rates well
above 200 and hold up in the 190s for several minutes! We all seem to be about the same fitness wise.
Is there something wrong with me?
A: Fear not the lower max heart rate.
Just like the answer
above, you can’t compare the heart rates of 2 different people.
While their heart rates go higher, you probably have a
higher stoke volume, therefore your heart rate doesn’t have to be
as high to produce the same cardiac output.
Rumor has it that Miguel Indurain’s
max HR was only about 155 BPM!
*This
effect is known as the Frank-Starling law
http://www.gpnotebook.co.uk/cache/1355808810.htm
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