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So I have been reading a new book "Body By Science" by Dr. Doug McGuff and John Little and it is incredible.  It is extremely well researched and in many ways makes some huge departures from conventional thinking when it comes to health and fitness.  But one of the more controversial claims that is made in this book is that "cardio" in the traditional sense as we know it is bad for your health...You read that right, it is BAD for you.  Now before you immediately get defensive about your morning walks, jogs and cycling routines, bare with me for a moment and let me explain in very clear, scientific terms why this is.  This claim isn't just some clever new trend or gimmick in fitness.  Its not some hot new celebrity endorsed fad.  This claim is a clear reflection of pure science and research.

 Defining Health & Fitness and Exercise

First things first, in this book they first begin by offering a clear and concise definition of the terms "health" and "fitness" and "exercise".  This may seem like a simple thing, but in reality very few sources have ever been able to offer up any real clear definitions for these terms.  Many sources often use the terms "health" & "fitness" interchangeably, which is wrong, as these two terms are distinctly separate and most definitely not one and the same.  As defined in the book, health is #1) the absence of disease and #2) a balance between the body's catabolic (break down) and anabolic (synthesis) states.  You see, our body is in a constant state of break down and rebuilding.  Metabolism is both catabolic and anabolic.  Normal healthy functioning cells within our body die and are replaced.  That’s part of the circle of life so to speak.  Anytime we have an imbalance in either a catabolic or anabolic state, we develop problems.  Cancer is a perfect example of an imbalance of anabolism, cells continue to grow and proliferate without any mechanism to stop them.  So, health is a proper balance of states.  Fitness on the other hand is defined as our ability to adapt to various stressors.  Whether that stressor is a physical demand such as running a marathon, or the threat of a foreign invader such as a virus or bacteria.  Our ability to adapt to these stressors is a reflection of our level of fitness.  Despite what some may think, these two are not directly proportional to one another.  You can have such a thing as an individual who is highly fit but yet extremely unhealthy.  A prime example of this is a marathoner who has knees that are full of degeneration from the miles and miles of wear and tear placed on them from all those years of running.  This is obviously an extreme example, but you get the idea.  Exercise is defined as any activity in which a positive physiological adaptation is brought about which enhances both health and fitness without undermining the former but improving the latter.

A (Very) Basic Overview of Biochemistry...Relax, It Won't Put You to Sleep, I Promise!

Before I can explain why "cardio" in the traditional sense is bad for you, I need set the stage first by explaining some basic principles of biochemistry.  So, first, our body's fundamental fuel source is glucose.  We use glucose to produce the primary energy currency that our body uses called ATP (adenosine triphosphate).  The body can store glucose in a few areas and different forms.  Two places it stores glucose is in the liver and in muscle tissue.  Glucose is stored in these tissues is in a form called glycogen, which is in essence a compound of glucose molecules.  Another common way in which glucose is stored is by being converted through a series of reactions into body fat.  To extremely oversimplify it, if we want to burn body fat, we must first use up the stores of glycogen within the muscle tissue and the liver.  When we liberate the glycogen from these tissues we begin a process called glycogenolysis, which basically means we are converting glycogen back into glucose to be used as fuel.  The catch is that in order to access and utilize these stores of glycogen we must reach a level of intensity in our exercise sufficiently high enough to signal the right hormones to release the glycogen to be converted to glucose and used as fuel.  When we do this and create a deficit of glycogen stores our body is then put into a state where it can begin burning fat and begin the process of storing glucose in the form of glycogen rather than converting it and storing it as body fat.  Again, let me stress that the key here to accessing these glycogen stores is through exercising at a sufficiently high level of intensity.  The old saying "slow and steady does it" type of cardio is not correct in this case and will not access these glycogen stores.

Calories Burned Does Not Equal Fat Burned

There are 3,500 calories in a pound of fat.  So this means that if we were literally to melt away fat through simple caloric burn, then we would need to run around 35 miles just to burn a pound of fat!  That sounds a bit crazy to me.  In spite of this however, people burn fat all the time through burning a few hundred calories at a time.  And on the other hand, people steadily jog on the treadmill for hours and not burn any fat.  How does that work?  Well, the answer lies in the most fundamental ways that our body transforms itself.  Whether it is building muscle, toning up, burning fat, developing greater speed, etc.  All of these transformations are done by means of hormonal signaling.  We don't burn fat by simply burning the caloric equivalent.  We burn fat by exercising in such a way that we are able to activate the right hormones at a sufficient level such that they begin the various metabolic processes that either burn fat, build muscle or whatever.

 Why Cardio is Bad

Cardio in the traditional sense, i.e. walking, running, or biking at a slow and steady pace is bad for several reasons.  First and foremost, exercising at these low levels never allows your body to reach a state of exercise of sufficient intensity so as to signal the necessary hormones to create the various metabolic reactions responsible for burning fat, building muscle, or other transformative changes.  In order for these hormones to be released you need high intensity exercise.  The slow and steady cardio doesn't liberate the glycogen stores in the muscle fibers and liver and therefore as a result any excess glucose in your body gets stored as fat, or even worse creates insulin resistance and inflammation throughout the body causing a host of health problems.  One of the fastest ways to manage blood glucose levels is through high intensity exercise.  Because in these high intensity exercises you release these glycogen stores any glucose thereafter is shunted into the liver and muscle tissue to replenish these gylcogen stores.  This isn't something that just last an hour or two afterwards by the way, these effects last for days.  Another reason cardio is bad for you is that it often times creates a tremendous amount of wear and tear on the body, such as in long distance running.  I know avid runners will hate this idea, but the truth of the matter is that running is a tremendously high impact activity that puts a lot of abuse on our frame.  What you are dealing with here are your classic repetitive stress injuries.

  True Cardio

Its funny but the term cardio has become synonymous with running or other slow and steady exercises.  The truth is that slow and steady type exercises really just train your heart to pump the exact same way, slow and steady like a metronome. The healthiest hearts are ones that are the most efficient pumps.  To be an efficient pump your heart needs to be able to pump enough blood to the areas of your body that are needed when they are needed, not just a nice gentle rhythmic bump.  This sort of "pumping on demand" way of viewing the heart is known as heart rate variability.  The greater the heart rate variability means that your heart can quickly and efficiently go from a resting state to a state of demand without much difficulty.  Studies have shown that greater heart rate variability is a valid indicator of overall heart health.  In addition to this several studies have shown a strong connection between high heart rate variability and improved brain function and self control.

Another way in which heart health is actually assessed is through a measurement known as your ejection fraction.  This measures the amount of blood your heart is capable of pumping out in a heartbeat.  If you are looking to create a more efficient pumping mechanism, your heart needs to be sufficiently challenged.  This can be done a few different ways.  You can work large muscle groups under sufficient load as to create a high demand on your heart.  These can be things like squats, lunges, or other large muscle group exercises.  Muscles need blood to function, and the simple truth of the matter is that the more demand we place on large muscle groups, the harder the heart will be challenged.  So in reality, true cardio is any activity that places a high enough demand on the heart as to require it to pump a high volume of blood to various areas of the body.  Another way is through high intensity interval training.  This type of training can be found in a variety of different fitness programs.  I mentioned in a previous article that crossfit is a great example of this type of high intensity training.  The beauty is that numerous studies have shown that you don't need to do these sorts of high intensity exercises for hours each day to see major benefits.  In most instances you only need a short duration to get maximum benefits.  I am talking literally a few minutes each day.

What Now?

Specific exercise prescriptions are way beyond the scope of this article (I know its already been a long one!) but the point that should be abundantly clear by now is that in order for you to get the greatest benefits of exercise, you need to work at a sufficiently high enough level to create the right hormonal signals.  This doesn't mean that you need to kill yourself tomorrow.  It simply means that taking the slow and steady approach to fitness will not only sell you short, it will ultimately undermine your health and fitness goals in the long run.  So, if you aren't getting the results you want, whether that’s losing weight or building muscle, consider the fact that maybe you aren't hitting a high enough point of intensity as to signal the necessary hormones to make those changes.  I highly suggest a great starting point is by reading the book "Body By Science".