Do We Actually Need To Do “Cardio”?

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Female athlete in mini shorts warming up on treadmill on beautiful sunny morning

About 99.999999% of fitness enthusiasts, athletes, bodybuilders and average gym goers believe that cardio is, unquestionably, necessary for overall health and fitness. But, have they ever stopped to wonder why they thought that was true? Fitness is very susceptible to trends and vogue, but it seems this dichotomy between cardio and other forms of exercise has survived despite somewhat obvious physiology and biochemistry. I’m going to debunk it for you with EVIDENCE.

The Origin of Cardio

What does the word “cardio” even stand for? What some people may not realize is that it is short for the word cardiovascular; referring to the cardiovascular system of the human organism which is responsible for circulating blood, nutrients, oxygen, hormones and other valuable resources throughout the body. This includes the heart, blood vessels, veins, arteries etc.

Over the last 50-60 years, we’ve been classifying activities such as walking, jogging and biking as “cardio” workouts; largely as a result of the “aerobics” movement started by Kenneth Cooper in the 1960s (this is something us HIT guys love to whine about). Ken Cooper believed that in order to improve your cardiovascular system through exercise, you must selectively train the aerobic energy system though low intensity and high volume activity. He created the term “aerobics” to categorize his recommended exercise modalities which later became known as “cardiovascular conditioning” and is now referred to as “cardio”. This is why many people believe that 1-2 hours of aerobic activity per day is necessary for cardiovascular fitness.

The Aerobic Respiratory System

Now, let me explain to how the energy systems in your cells work so you can better understand where Ken Cooper was (falsely) coming from. In your muscles, you have muscle cells. The muscle cell is responsible for turning substrate (glucose, fatty acids) into usable energy in the form of ATP. As the glucose enters the cell, it first goes through anaerobic respiration or Glycolysis; a quick process where substrate is broken down into pyruvate yielding just 4 ATP. ATP is the energy currency used by our bodies for cellular functions, including mechanical movement of muscle.

Well, over the course of our evolution, we developed a symbiotic relationship with a little organelle called the mitochondria which consumes our byproduct of anaerobic respiration (pyruvate) and in turn, produces usable energy for the entirety of the cell in the form of 36 ATP. This sequence is called aerobic respiration or the Krebs Cycle.

As you can see, anaerobic metabolism FEEDS aerobic metabolism. Aerobic metabolism cannot perform without the substrate of anaerobic metabolism with glucose as its original substrate. This is where Ken Cooper caused confusion with the promotion of aerobic exercise. Ken presumed that the aerobic system was somehow directly responsible for stimulating the heart and cardiovascular system when in reality, both systems work together like a pair of gears.

The catch is, anaerobic respiration can turn out much more pyruvate than the mitochondria can take in to use in aerobic metabolism. Once you crank up the anaerobic process too fast and too much pyruvate builds up than can be used, it turns into Lactic Acid; this is the burning sensation you feel in your muscle. The Lactic Acid then circulates through your body and comes back to be consumed in the mitochondria later on, often when you’re resting after a tough workout.

That’s right, once you’ve built up lactic acid from an intense workout, it’s still churning your aerobic system while you’re sitting down resting. Now that’s my kind of “cardio” workout.

Any Muscular Work Is Cardio!

Any time you perform mechanical work with muscle, whether is walking, sprinting, lifting weights or pushing granny through the grocery store, your cardiovascular system is working. In order to get the energy systems working hard, you’ll want to perform very Intense work with muscle.

Working the muscle as hard as you can ramps up both anaerobic and aerobic metabolism beyond what it is used to. In response, the processes within the cell will improve and become more efficient so that the heart and cardiovascular system does not have to work as hard to fuel the body. THIS is how your cardiovascular fitness improves. The heart itself does not really get “stronger”, but the processes that it supports improve at the cellular level.

Intense activities such as sprinting, HIIT intervals or weight training to muscular failure work the energy systems hard enough to produce an improvement. The traditional cardio activities such as jogging and walking will be somewhat effective at first, but eventually your body will adapt to them and they will become very ineffective.

When it comes to fat loss, most physical activity does not burn much body fat to begin with since glucose within the muscle is responsible for fueling most physical activity. But, if low intensity activity burns any body fat at all, it only makes sense that High Intensity activity would burn more! Mainly due to addition of adrenaline, but that’s a topic for another post.

That makes sense but… Prove it!

Okay I will.

Steele J, Fisher J, McGuff D, Bruce-Low S, Smith D. Resistance Training to Momentary Muscular Failure Improves Cardiovascular Fitness in Humans: A Review of Acute Physiological Responses and Chronic Physiological Adaptations.

This study is a comprehensive look at all of the surrounding scientific literature of resistance training, cardiovascular fitness and the acute responses and chronic adaptations it produces. After looking at dozens of research on cardiovascular exercise, the study found that simply performing resistance training to momentary muscular failure stimulated cardiovascular improvements just as effectively, if not more effectively than traditional cardio exercise.

So there you have it. It appears that there is a false dichotomy between cardio exercise and other modalities of exercise. An effective resistance training program, if done to momentary muscular failure will yield all of the benefits of traditional cardio WITH the addition of some nice lean muscle. The days of hours spend on the elliptical are over!