this 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 but you probably guessed it the human heart this is such an amazing organ this thing beats about a hundred thousand 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 its 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 a 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 got to 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 of it kind of like freeway 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 capillaries are tiny little exchange vessels that allow for exchange between the bloodstream and the surrounding tissue and in the case of exercising muscle oxygen demand is going up dramatically so that 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 deoxygenated 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 let me just open it up so you can see that clearly once we're in the left end 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 question 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 that flow and the output from the heart and one thing i want to mention when it comes to health wellness and participating in exercises that are going to create a strong and efficient 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this concept of the heart and vasculature delivering blood effectively to an exercising muscle now remember we used the quads in this example and as the quads began to exercise or any muscle for that matter oxygen demand increased dramatically so therefore a 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 a hundred gram 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 increase 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 400 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 increase in 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 could 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 a 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 vasoconstriction of the peripheral arterials and what does that mean well those tiny little arteries those arterials 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 arterials feeding the muscle tissue itself those are 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 definitely 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 onto 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 back to the heart so we're going to get a different results 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 volume 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 increased stretch myocardium or heart muscle responds 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 increased 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 athlete could push 400 milliliters through 100 grams of muscle 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 to 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 were to zoom in and zoom into 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 have 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 that we asked earlier in the video and we'll see you next time [Music] you