‘Cardio’ is meaningless – so please stop using the word

In my last post I explained why we shouldn’t ever use the word ‘cardio’ when we talk about exercise. Using ‘cardio’ to describe an activity that gets us out of breath is pointless. It is far better to think about exercise from the muscle’s point of view. If we are exercising the big muscles in our lower body continuously for at least 15 minutes (like running or cycling) – and getting out of breath – then we are doing ‘aerobic’ exercise. (please don’t call it cardio)

Boot camp training (the continuous sequence of short-burst activities) isn’t a very good way to build muscle mitochondria and elicit aerobic adaptations. So, is there any point in doing boot camp-style training? Have the Army got it wrong? And why do weight lifters get out of breath anyway?

Is Boot Camp training pointless?

During boot camp training, the reason you are breathing hard is because you have just performed anaerobic exercise. Anaerobic means “Without Oxygen” (how is that possible? See my post ‘your muscles are out of breath but you’re getting fitter’). This absence of oxygen means muscles make energy without using their mitochondria. This should all sound familiar if you’ve been reading my previous posts. But let me just explain that the reason your chest is heaving after the sprint, the fence jump and the push-ups is because of the by-products of anaerobic cellular respiration – lactic acid.

Camp Taji obstacle courseYour body can handle this nasty acid in your blood stream and produces a by-product of carbon dioxide (Google ‘pH buffer in the body’ to find out more). When you work your muscles super-hard during anaerobic exercise, carbon dioxide builds up in your blood. Your breathing therefore speeds up, in part, to get the CO2 out of your blood stream. The greater the concentration of CO2 in the blood, the more your breathing will increase. Ever noticed how hard weight-lifters breathe? They’re breathing out all the CO2 generated from anaerobic exercise.

In contrast, aerobic exercise is gentler. Something you can keep doing nonstop. We can call “nonstop” exercise something else if you prefer; “steady state” might be a better term to help you grasp this concept. I hope the difference between aerobic and anaerobic is getting clearer. And I hope you understand the different adaptations that happen as a result of stressing your muscles aerobically, verses anaerobically (if you don’t then it might be worth checking out my article on the different types of muscle we have in our body)

I also hope you can now see that the “symptoms” of exercise, the hard breathing and pounding heart, don’t always result in the same muscular adaptations. I will elaborate in forthcoming posts but if you are still fuzzy on why there is a difference to your muscles between steady state jogging vs playing tennis and breathing hard, then let me offer another comparison of something that makes you breathe hard:

A doorbell rings!

Imagine you are sitting at home one night alone and the doorbell rings. You go to the door and no-one is there. You carry on your business and hear the door bell ring again. You answer it a second time and no-one is there. It happens a third time and still no-one is there. This happens forty more times over the next hour. After the fourth doorbell ring your heart rate shoots up. You are breathing hard. You are sweating profusely. You are shaking all over.

You call your neighbor, who happens to be an electrician, and discover that there was a short in your door bell and there was nothing to be afraid of. You feel exhausted but console yourself: “Well, at least I got my Cardio for the day”. WRONG!!!

As in this instance, an anxiety attack will not cause any of the positive adaptations we see from exercises. The point is that the symptoms of exercise can happen from different reasons or stimuli. Try to think about the way the symptoms are caused to figure out what the adaptation will be (if any).

Is it clearer now? The term ‘cardio’ tells us nothing about the type of stress we are putting on our muscles. People use the term as a synonym for “out of breath and a racing heart”. We need to be specific in our use of the language to have a better understanding about the biology. Please try to think in terms of ‘aerobic stress‘ and ‘anaerobic stress‘ on your muscles.

In my next post I’m going to explain what happens when you do aerobic exercise at very high intensities. And I’m going to explain the fuel sources your body uses as your exercise intensity goes up. This will give you an understanding of what goes on in your muscles as an exercise goes from being aerobic to anaerobic…


For tips on improving your aerobic fitness check out my article ‘Get Fit in 3 Steps: Your recipe for more Mitochondria’.

You can read all of Matthew’s series on fitness here

Front slider image: Newt Gingrich – He-Man of South Carolina by DonkeyHotey on Flickr

Article by Matthew Linsdell

February 29, 2012

Matt is a certified personal trainer and has a degree in Environmental Science. He calls himself an evidence-based trainer, because training is a field which is littered with well-disguised pseudoscience – his emphasis is always on teaching the biology behind exercise. He lives at the edge of the beautiful and expansive Gatineau Park in Quebec and works across the water in Ottawa, Ontario. If he’s not out walking his two pit bulls, you’ll find him doing press ups with insanely large weights on his back. Follow Matt on Twitter at @smartfitmatt.

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9 thoughts on “‘Cardio’ is meaningless – so please stop using the word”

  1. I may have to take the word “cardio” out of my language. I like this a lot, and it also explains why BOTH forms of excercise (aerobic and anaerobic) are needed. Cross-training like yoga and resistance training have helped my running so much.

  2. I’m glad to hear this Suzanne. And you’ve just inspired me to write an article about cross-training.

    1. This article is written in an easy to understand way to illustrate how carbon dioxide builds up in the blood and causes someone to breather harder.

      I read the link you pasted. Is it meant to be an explanation as to why this article is “not really accurate at all”?

      Could you please elaborate as to why this isn’t accurate?

      1. Here is a start: http://people.eku.edu/ritchisong/301notes6.htm.
        There is a great recent review on pubmed I will dig up that further shows that respiration during exercise is likely a feedforward neurally driven process.
        Your position that lactate is a waste product is false as it it an important fuel source and “messenger”. Even the increased acidity associated with exercise has been shown to potentially improve performance, and lactate is only associated not causal of the acidity.
        Lastly, recent compelling research suggests that fatigue is also a neurally driven process.

        1. Hey Roku I think you’ve missed something important. I never said that lactate was a waste product. I stated that lactic acid is a by-products of anaerobic cellular respiration. Do you want to take issue against this? Do you know the difference between lactate and lactic acid?

          1. “But let me just explain that the reason your chest is heaving after the sprint, the fence jump and the push-ups is because of the by-products of anaerobic cellular respiration – lactic acid.

            Your body can handle this nasty acid in your blood stream and produces a by-product of carbon dioxide”

            First, it is never produced as lactic acid. Like you stated it is lactate, an energy substrate, not a waste product. ATP hydrolysis produces H+ as well, which could be just as responsible for “acidity,” which I do not think is the reason for the feeling of fatigue.

            It may be a by-product in yeast, but certainly not in humans.

            All I am saying is respiration is not a simple black and white process and during heavy exercise it is NOT CO2 driven, which is what you have stated in your article, correct?

            I posted my reasoning.

  3. Roku I’m finding it difficult to understand exactly what your dispute is over these last few comments. But I can answer this one. Carbon Dioxide concentration in the blood stream increases respiration. Yes, that is what I am saying. And carbon dioxide builds up in the bloodstream because of the buffering effect caused by the bicarbonate buffering mechanism. Respiration speeds up to dissipate the build up of Carbon Dioxide. I don’t know why you’ve mentioned fatigue twice. I don’t think we’re talking about fatigue. I’m happy to discuss this further but you need to stick to one issue at a time.

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