Video is sponsored by Athletic Greens. Find the link in the description below. What weighs
8 to 10 ounces, can fit in the palm of your hand and pumps thousands of liters of fluid
per day? Well, you probably guessed it, the human heart. This is such an amazing
organ. This thing beats about 100,000 times per day which translates to approximately
35 million beats per year and about 2.5 billion beats in the average lifetime.
Relative to its size, the heart packs quite the punch and when we exercise,
we further increase the demands placed upon the heart. So, in this video,
we're going to talk about some of the amazing adjustments that the heart and cardiovascular
system make when say you go from a resting state all the way up to a state of intense exercise.
We'll also discuss some of the amazing adaptations that can occur within the heart
when you continue to exercise. I think the numbers
and the changes will astound you. So, let's jump right into the heart.
So, let's start by painting the overall picture of the heart and its relationship to the muscle
tissue that we'll be using during exercise. Now, all of us have a pretty good idea that
the heart is a pump and it's main job is to pump blood to the tissues of the body.
Now, keep in mind, we're going to be focusing on muscle tissue in this example
but these principles can be applied to the other tissues in the body.
So, let's take a look at this heart dissection we have on the tray here and you can see we've
done some dissection work here. We've opened up into a chamber here as well as the chamber here
and you can see the large blood vessels that we'll talk about in just a second.
Now, when we're talking about delivering blood effectively to muscle tissue,
we've gotta talk about the most powerful chamber of the heart called the left ventricle
and where we were looking earlier, this is an inside view of the left ventricle,
the most powerful chamber of the heart because it has to pump blood to the entire body and
you can see how thick the muscular wall is especially when we compare it to the thickness
of the right ventricle which only has to pump blood to the lungs in as you can see is thinner.
But this more powerful left ventricle, when it pumps, it's going to pump blood through a valve
and into this tube that you can see the probe coming out here called the aorta.
Now let me show you the aorta on this other cadaver dissection here. The aorta you can
see and appreciate how massive it is here and how much elastic recoil it has. This thing
is the size of a garden hose. It's the largest artery in the human body. Keep in mind,
arteries take blood away from the heart and the aorta as this main artery is going to
have multiple branches of other arteries coming off it kind of like free off ramps
to deliver blood to the head and neck, the upper limbs, the trunk, and even the lower limbs.
And speaking of the lower limbs, let's use some muscles like the quads that we all
know and love because they get involved in all sorts of different exercises to help us complete
this picture of the heart's relationship to getting the blood to the muscle tissue.
So, here you're taking a look at an anterior or a front view of a right thigh.
You can see some of the quadricep muscles exposed. I'm going to actually reflect this
really cool muscle called the sartorius so that we can see the amazing femoral artery.
Now, you have to imagine as blood is passing down through the femoral artery, there's going to be
other smaller arterial branches coming off and penetrating into the surrounding muscle tissue
and as those arteries continue to branch, get smaller, and penetrate the tissue, we're
going to start changing the name from artery to arterial and an arterial is just a smaller artery.
Those arterials will then flow into another blood vessel type called the capillary
and this is where the magic happens. Capilaries are tiny little exchange vessels that allow for
exchange to the bloodstream and the surrounding tissue and in the case of exercising muscle,
oxygen demand is going up dramatically. So, oxygen will diffuse from the bloodstream
into the muscle tissue while at the same time, all the carbon dioxide and metabolic waste
products from the muscle will diffuse into the capillary and therefore the bloodstream.
So, you get this flip flop or exchange between the two. Now, that capillary is now said to have
deoxygenated blood because it's low in oxygen but high in carbon dioxide. It will then flow out into
a venule, which is a tiny vein, then drain into a little bit larger veins, leave the muscle tissue
and instead of going into the femoral artery, we would drain into a vein like the femoral
vein and we say that veins go back to the heart and that's exactly where we're going.
All that deoxinated blood from the body is going to flow into this chamber
that we refer to as the right atrium. The right atrium will then pass that blood into the right
ventricle where the probe is here which we talked about earlier which will take blood to the lungs
which is really important to get rid of the carbon dioxide, get more oxygen back into the blood.
That oxygenated blood will now go back to the left atrium here and let me just open
it up so you can see that clearly. Once we're in the left atrium, that blood can then pass
where we started back into that powerful chamber called the left ventricle.
Now you may have noticed I didn't mention any of the specific names of the valves
but that's because that's our quiz que of the video. Can you name all four valves of the
heart? Post them in the comments and we'll pin a comment at the top with all the correct answers.
Now, keep in mind that this flow that we just discussed is going to be occurring at rest
as well as during exercise. It's just during exercise, we're going to see dramatic changes in
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So, the sustained energy levels that I experience throughout the day as
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So coming back to this concept of the heart and vasculature
delivering blood effectively to an exercising muscle. Now remember we use the quads in
this example and as the quads began to exercise or any muscle for that matter,
oxygen demand increase dramatically. So therefore, need for more blood to that muscle tissue but how
much of an increase in blood are we talking from a resting muscle to an exercising muscle?
Well let me give you some numbers - if we were to take a muscle at rest and look at the average
blood flow we'd see that it was about three to four milliliters per minute per 100 grams of
muscle tissue. So in other words, if we were to take 100 grams segment of this quadricep
muscle here, at rest we'd see about three to four milliliters passing through in a minute but when
we exercise, that can up to 200 milliliters per minute in that same 100 grams of muscle tissue.
Now if that doesn't surprise you or impress you, they've actually measured in the quadriceps of
elite marathon runners a change of up to 400 milliliters per minute in that same
100 grams of muscle tissue. That's crazy! To give you a visual on that - here's four
milliliters of fluid here that you can see finally focusing in, we've also got 200 milliliters here
and four hundred milliliters there. That's a crazy change in blood flow through an exercising muscle.
But what is accounting for these changes? Well, we're going to talk about what we'll call three
circulatory adjustments that the body performs to accommodate or to increase this blood supply.
One is an increasing cardiac output. Two, we're going to see vasoconstriction of peripheral
arterials and three is somewhat similar to two where we'll see a forceful contraction
of the walls in a lot of the veins throughout the body and we'll explain some of the similarities
and differences between two and three but let's start with number one, increasing cardiac output.
Cardiac output is the amount of blood pumped out of the heart in one minute and there's two main
factors that influence this. One is the heart rate or the number of heartbeats per minute
and two, stroke volume. Stroke volume is the amount or the
volume of blood pumped out during each beat and both of these will increase during exercise.
Most of us have a pretty good idea that when we go running around and exercising,
our heart rate will go up and during intense exercise, we can see heart rates close to 200
beats per minute. Now, many of you have probably heard of like calculating your
max heart rate and there's a general rule of thumb of 220 minus your age. So, in theory,
we can have a 20 year old that would have a max heart rate of about 200 beats per minute.
Now, again, the stroke volume is this other thing we have to talk about.
The volume of blood that's going to be pumped out of this left ventricle during each beat.
The left ventricle, the force of the contraction can almost double during exercise and so
therefore, the volume of blood that's going to be pumped out each beat will increase.
So, let me give you guys some numbers. We've been talking numbers during this
video but this is going to help solidify this even more I think. The average adult
male, healthy adult male has a cardiac output of about 5.6 liters of blood
per minute during rest. Female of similar age would have about 4.9 liters per minute.
So, we're around that five-liter range but during exercise, let's say we took a person who has a
functioning, normally functioning heart but isn't exercising a ton consistently, their heart could
go up to about 13 to 15 liters per minute during exercise. So, that's still a pretty dramatic
change but again, when we talk about those people who are consistently exercising, training for
marathons and elite athletes, we can see cardiac output go up from 30 to 40 liters per minute.
These are amazing adaptations the heart can do when we consistently
challenge it and exercise it through consistent activity and we'll get more
into these long-term adaptations that can occur through consistent activity
later because we still need to cover the second and third circulatory adjustments.
That second circulatory adjustment was vasal constriction of the peripheral arterioles
and what does that mean? Well, those tiny little arteries, those arterioles
will constrict and narrow therefore decreasing the blood supply
to these non-muscular tissues like the intestines or say like the skin.
Now why would the body do this? Well we're essentially taking or shunting or "lending" more
blood to the muscle tissue that's exercising in this moment. If the goal is to run up a
mountain or exercise, then we're not going to divert extra blood to say like the intestines
to digest or absorb your last meal. Now, of course the arterioles feeding the muscle tissue itself,
those going to stay open or vasodilated and that's controlled at the actual local level within the
muscle tissue itself but there's two exceptions we need to discuss regarding this vasoconstriction.
First, the brain. It doesn't make sense to constrict the blood vessels to the brain.
Those are going to stay open because the brain is going to participate in coordinating
skeletal muscle activities as well as say like making split second decisions say in sports.
The other is the heart. The coronary arteries are something you do not
want to constrict. You want these blood vessels going to the heart muscle itself
to stay open so that cardiac output can be maintained at the necessary level.
Now on the circulatory adjustment number three, the powerful or forceful contraction
of the muscular wall of the veins throughout the body. So, we're getting to this idea of
vasoconstriction again and you might be thinking, "well, that's similar to adjustment number two"
but remember, arteries and arterials take blood away from the heart whereas venules
and veins take blood backed the heart. So, we're going to get a different result here.
So, let's take a look at this cadaver dissection and use this femoral vein as an example again and
imagine blood returning to the heart through this vein but let's also imagine we get this powerful
contraction of the muscular wall of that vein. That would decrease the amount of blood pulling
in the venous system as well as force blood back towards the heart or in other words, we'd say
increases venous return and therefore, more blood going to the heart and we have to think
about this one key concept here. The amount of blood that's being returned to the heart,
that same amount needs to also be pumped out of the heart
because we need to have inputs equaling outputs in this situation.
We don't want to have this traffic jam or this backup of blood because that would
create a problem. Luckily, the heart has a built-in mechanism that whatever amount of
blood is returned to the heart, that same amount is automatically almost reflexively
pumped out of the heart. This is referred to as the Frank Starling Law of the Heart which
essentially states as an increased amount of blood returns to the heart that will cause
stretch on the walls of the heart and the myocardium or the heart muscle will respond
to that by contracting more forcefully to expel that extra amount of blood that was returned.
So in other words we get an increased blood volume, increase stretch, myocardium or heart
muscle response by contracting more forcefully and you can see that this circulatory adjustment
number three is really closely related to the first adjustment we mentioned with cardiac
output because as that increase blood volume comes back to the heart, the heart reflexively
contracts to force that excess blood that came out and thereby increasing cardiac output.
Up to this point, we've talked about cardiovascular adjustments that occur
in the actual moment of exercise. Yet, throughout the video, we've alluded to these
long-term adaptations that could occur with the heart
and other cardiovascular structures especially in well-trained individuals and elite athletes.
So, what are these adaptations and what makes it so an elite could push 400 milliliters through,
100 grams of muscles that we talked about earlier or increase their cardiac output
to 30 to 40 liters per minute? Well, a big part of that answer lies within
the myocardium of the heart. So, as we already know, the myocardium makes up 95%
of the heart wall and is essentially the heart muscle that is going to do all of the pumping.
Now, in elite athletes, they've seen increases in myocardial mass of up to 50 to 75%. So, this is
definitely going to get thicker and stronger. Now, one thing we have to think about here is
that the actual myocardium or muscle tissue is made up of multiple cardiac muscle cells.
So, when a tissue gets bigger or larger, we kind of have to think, okay, is it going to do it by
increasing the number of cells or by increasing the size of the cells that we already have?
Now, one of the interesting things is that the myocardium or the muscle cells that make up
this myocardium, they cannot divide or undergo mitosis and just a little bit of a side note,
that's why I tell my students that a heart attack is so detrimental
because any of the cardiac muscle cells that you kill potentially during a heart attack
cannot be replaced and typically gets replaced with scar tissue instead.
So, that leaves us with the other option to increase the myocardial size and that is
through increasing the size of the cells that we already have through hypertrophy
and a larger cell is a stronger cell and so overall this myocardium gets stronger
and can therefore contract more forcefully.
So, let's give us this idea of or a scenario of how that would make sense in the real world. Let's
say you started training for a marathon or a half marathon and in the initial stages of training,
you get to this certain pace and you stay at this steady pace and your heart rate's at 165 beats per
minute and over time as you get in better shape or your myocardium gets a little bit larger and
stronger, maybe at that same pace, your heart rate might start going down to 155 beats per minute
and that's because when the heart muscle is stronger, that increases the stroke volume.
So, each beat is more efficient and pumps out more blood per beat. That's also why people who
are training tend to start seeing a decrease in their resting heart rate. Instead of 60 beats
per minute - needing 60 beats per minute to get a certain amount of blood out, you might only need
55 or 50 after you've trained longer and you've had a more efficient heart or stronger myocardium.
The other adaptation we'll see is an increase in microvascularization or in other words,
the blood flow to the muscle tissue. So, let's use this example of this quadriceps muscle here
and if we are to zoom in and zoom in to this muscle tissue,
again, we would see those tiny little blood vessels that we referred to as
capillaries and as someone exercises, the number of capillaries increases. So,
therefore, we even more blood able to penetrate the muscle tissue and therefore more oxygen.
Now, we could go over the adaptations that occur in the actual muscle tissue. However,
I don't think you guys want to watch a 40-minute video so we'll save
muscular adaptations for a later video but hopefully you guys learned something amazing
about your heart and cardiovascular systems that you didn't already know.
Be sure to check out that link from Athletic Greens below and if you feel like it,
you can like, subscribe, and be sure to leave a comment especially one with that
quiz question we asked earlier in the video and we'll see you next time.