Cardio Is Not About Your Heart!

by J Braun & Malia Steele

We are all told to do cardio to strengthen our heart and aerobic exercise to strengthen our lungs. Is the goal for cardio/aerobic exercise to strengthen these organs?  Is that even possible?  Is their function, or lack thereof, the reason we breathe so hard?  Should I just keep asking you questions?

All these questions historically have us automatically assuming that cardio/aerobic exercise is related to the heart and lungs.  We’ve even named them based on these notions: cardio and/or aerobic activity.  Over the decades several studies have examined the relationship between physical activity, physical fitness and cardiovascular health. (If you don't believe me just type “exercise” and “your heart” or “exercise and cardiovascular effects” in Google.)  

So yes, researchers, doctors, physical therapists, trainers, Dr Oz, Oprah, your-mother's-friend-that-saw-that-thing-on-TV-last-night will all tell you that cardiovascular exercise strengthens your heart and lungs, and you need to train your heart and lungs to be “healthy”.  I call bullshit on that.  You are NEVER training your heart, and you are NEVER training your lungs.  Chew on that for a second.  Shocker right?

Sorry to tell you this, and people have repeated and preached this huge misconception since before Richard Simmons put on his first pair of dolphin shorts.  Don’t worry, we are here to set you right.  When you are doing your cardio/aerobic thing, you are not training your heart, you are not training your lung, you are training……(let the tension build)..... MUSCLE!!!!  The relationship between cardio/aerobic exercise and your heart and lungs is that your heart and lungs are your muscles’ peon employees, and only respond to your muscles’ demands.  Your heart only beats faster when exercising because your muscles need to accomplish whatever 5K-like task you’ve put in front of them, and to do that, they need some O2-enated (not a real word, so don’t bother searching) blood.  Which is where your lungs come in.  To draw in some O2, and get rid of some CO2.  

That’s the most palatable version of this we can come up with.  We are going to slightly step-up the sciency stuff below (very slightly, we don’t want to lose everybody.  So science-nerds backoff!!!)

The energy (ATP) producers of your muscles’ cells that we will be focusing on are called mitochondria. The amount, or density, of these little guys will dictate the volume and intensity of challenge that your body can respond to. The mitochondria present are vital in not only providing the energy to the muscles, but also play a key component in muscle size and function. Once a challenge is introduced, your muscles contract to meet said challenge.  The intensity and duration of the task at hand is going to dictate the energy systems required for response.  Think of it in car terms (this isn’t the best analogy, but just go with it):  You press the accelerator of your IROC Z (I’m from North Jersey, it’s what I know), and as the car accelerates, you need to shift gears to keep increasing speed.  The longer and faster you need to go, the more gears you need to go through. If you slam the pedal to the floor, and just need to beat the Guido to your right to the next light, you don’t need many gears, but if you are racing him on the highway down to Seaside Heights, you need all your gears.  This is kind of the way your muscles will be recruited for challenge.  To get to and use those “higher gears”, you need enough mitochondrial density and the Kreb Cycle (look at it you want to, super geeks.  Others, carry on).  This is finally where your heart and lungs get involved.

It is the job of the lungs to oxygenate your blood and remove any carbon dioxide, and then it is the job of the heart to deliver this blood to your muscle. The key point of this is that the main physiological benefit of cardio and aerobic exercise is that muscles gain contractile strength and efficiency, not that hearts get “healthier” or lungs have greater “lung capacity”(if that shit even exists).

As one’s muscle cells increase mitochondrial density, their ability to use oxygen improves (Kreb cycle again), and regular daily activity can be performed with less fatigue, meaning less heavy breathing and longer exercise duration time. There is also evidence that cardiovascular “extended-duration-low-intensity-strength-training” (doesn’t that just roll right off your tongue?) can elicit a response in your blood vessels’ ability to dilate (become bigger), which is a response that is consistent with better vascular wall function, and an improved ability to provide oxygenated blood to the muscles during exercise.

Your muscles use glucose and ATP for contraction, just like we use food to gain energy.  To create more ATP, your muscles need to recruit more muscle fibers, which produces an increase in active mitochondrial density resulting in your body needing extra oxygenated blood. In response to the increase in muscular demand, breathing increases and your heart starts to pump more blood to your muscles. Here is where “Big-Boy Syndrome”(obesity) can get in the way.  If you have a big heart (which big-boys do, just look at the picture), it requires more energy and effort to pump the blood to your muscles, which is a common reason for early exercise fatigue in big-boys.  Their non-functioning mass (fat) also acts as a vasoconstrictor (real word), restricting blood flow and also increasing the force your heart needs to contract in order to circulate your blood, which yields an increase in heart size and thickness (not something you want to get buff).  

In simple words, the stronger and more efficient your muscle tissue is, the more O2-enated blood can get to your muscles.  The more overweight you are, the more trouble you are in. Don't believe me, take a look at the different sizes in hearts of a healthy person compared to an obese person. Notice that the bigger the heart size, the harder it is to pass oxygenated blood to the muscles, and even harder it is to activate mitochondria to provide the energy we need to continue to workout, resulting in greater fatigue in less amount of time.

Basically what we have been told since day one is that cardiovascular “extended-duration-low- intensity-strength-training” is all about your heart and lungs. False. Neither the heart nor the lungs are what enhance/strengthen your performance.  It is all about muscular demand, and your muscles’ ability to utilize the increased amount of O2-enated blood sent.  The bigger and stronger your heart is probably means you suffer from BBS (big-boy syndrome) and the harder it is to pass the blood along to the muscles. It is all about the ability of your muscles to process the oxygen and turn it into energy to use during your workout, and to then signal the heart and lungs when more oxygen is needed; it’s fundamentally all about the energy utilization within your active muscles.  

Think of your lungs as the first transporter - the one that changes your blood into oxygenated blood - and then, in turn, heads to the second transporter - your heart. Your heart acts a necessary transporter to the main event - your muscles. Changes within your active muscles are essential to the metabolic, and functional alterations that support enhanced performance changes observed after cardio and aerobic exercise “extended-duration-low-intensity-strength-training”.

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