Think you know what aerobic means?

By May 6, 2015 November 29th, 2016 Exercise, Fat-Burning Journal

Your Brain Might be Telling You One Thing, but Your Body is Saying Something Different

Most people think they know what aerobic means, or so they say. When asked, many associate it with breathing, air, or oxygen. Or they confuse it with “cardio” at the gym, where you can also find aerobic dance classes and pool aerobics. In fact, aerobics is a relatively recent form of exercise. It’s not even 50 years old, although humans have been doing it for millions of years. In the late sixties, Dr. Kenneth H. Cooper, an exercise physiologist for the San Antonio Air Force Hospital, Texas, coined the term ‘aerobics’ to describe the system of exercise that he devised to help prevent coronary artery disease. Dr. Cooper originally formulated aerobic exercises specifically for astronauts, but soon realized that the same set of exercises such jogging, running, walking and biking are useful for the general public as well, especially those suffering from being overweight, who are more likely to develop various heart diseases. He put together all of the aspects and methods he founded in his book Aerobics, which came out in 1968 and became an immediate national bestseller.

And what about anaerobic? What does this term mean? Being out of breath after short, intense and hard activity? Sprinting 100 yards on the track, going full-speed across the length of the pool, doing pushups until your arms and shoulders ache, or for many, climbing several, or sometimes even one, flights of stairs?

Once you see the difference between aerobic and anaerobic, this knowledge can help you build better health and fitness. So let’s start with a bit of history.

Dutch scientist Anton van Leeuwenhoek was the first to describe the microscopic components of muscle fibers in the middle of the seventeenth century. (He also was the first to observe and describe bacteria.) By the early 1800s, it was clear that two different types of human muscle fibers existed. Through the microscope, one showed a red color, and the other white. In humans, muscles are made different than in other animals such as birds. In chickens, for example, whole muscles are either red or white. The red muscles—the “meat”—are found in legs and thighs, while the white make up the breast. In humans, however, most muscles contain both red and white fibers (the exceptions are jaw muscles, which are predominantly anaerobic).

In 1863, French scientist Louis Pasteur coined the words aerobic and anaerobic. He was studying bacteria—and those that live only in the presence of oxygen he called aérobie. Aerobic comes from the Greek word “aero,” meaning air and “bios” refers to life. Some bacteria could not live with oxygen or air, and Pasteur called these anaérobie—anaerobic.

Around the same time in human physiology, the terms aerobic and anaerobic were used in relation to how the body obtained energy. They referred to two different complex energy transfer processes in cells—one that required oxygen (aerobic) and one that did not (anaerobic). More importantly, the source of energy produced in each muscle fiber was different. The red, aerobic fiber used fat as its source of energy. In order to convert fat to energy, this required oxygen—a reason for the large amount of blood vessels in the human body and in these muscle fibers—and for the cell components that aided this process which are called mitochondria. These iron-containing enzymes have a reddish protein called myoglobin.

In the white anaerobic fibers, none of these structures are needed. Energy is quickly generated through a process that uses sugar (glucose) as fuel that does not need oxygen.

As a result of further scientific research, these red and white muscle fibers in humans were also called type I, and type II, respectively. The red, type I aerobic fibers contract relatively slowly, and these would be called slow twitch. Their slow contraction would enable them to function for long periods—hours and days—without fatigue. This also allows them to support the body’s structures, especially the joints, bones, and arches of the feet.

The white, type II anaerobic fibers contract two to three times faster, and these were called fast twitch. They provide speed and power. But these attributes come with a price—they fatigue very quickly as their energy lasts only a very short time—a few seconds to about a minute (coincidentally, about as long as you can hold your breath).

In time, it was discovered that there was more than one type II muscle fiber, and these would be considered subdivisions of type II. Some of these fibers are pure fast twitch while others have a combination of both fiber qualities. Today, there are seven different fiber types, and as microscopic techniques improve, more may be discovered. But there are still two main types in humans—aerobic and anaerobic.

The list below is an overview of the function of each muscle fiber.

Aerobic Muscle Fibers

  • Red iron-containing cells, and packed with blood vessels
  • Slow-twitch sustains long-term activity
  • Resistant to fatigue
  • Uses (burns) fat for long -term energy
  • Supports the joints, bones, and overall posture and gait

Anaerobic Muscle Fibers

  • White cells with limited supply of blood vessels
  • Fast-twitch for short-term power and speed
  • Easily fatigued
  • Burns sugar for short-term energy

Exercise physiologists in particular refer to the aerobic system when discussing the red, slow twitch fatigue-resistant fat burning muscle fibers, and the anaerobic system referring to the white, fast twitch power and speed, sugar burning fibers.

So which system—aerobic or anaerobic—is working in you right now as you’re reading these words? The surprising answer is both. It’s easy to see that aerobic activity is important all the time—to maintain various functions such as posture and movement, long-term, consistent energy, and circulation. But even though we’re not sprinting or lifting heavy objects, the anaerobic system is always performing some basic tasks such as burning sugar. In fact, within the complex metabolic pathways of energy production, burning some sugar helps maintain fat burning. In addition, the anaerobic system is always prepared to take action if necessary—humans have a “fight or flight” mechanism waiting to act should the need arise.

The real question is which system is predominating—which are you relying on? Is your body burning mostly sugar and less fat? If this is so, your anaerobic system is the one turned on more than your aerobic body. While you may not notice this, especially if it’s an ongoing problem, but your energy and endurance is not what it should be, you are vulnerable to aches and pains, body fat content is too high, and you’re under too much stress as the anaerobic system is connected with our fight or flight stress mechanism. In short, your health is compromised.

Instead, you want long-term energy to be free of fatigue, maximum support for your joints and bones, injury-free muscles, good circulation, and increased fat burning to slim down. You want both optimal health and great fitness.

Aerobic vs. anaerobic exercises

Certain types of exercise will provide benefits that will build the aerobic system long term. I refer to these simply as aerobic workouts, meaning they will provide the stimulus to improve fat burning for more energy, continuous physical support, improved blood flow throughout the brain and body, and reductions in body fat. Easy activities, such as walking, running, biking, swimming, and the many types of aerobics classes can accomplish this if the intensity of these workouts is not too high. Your heart rate is an accurate indicator—lower heart rate exercise is aerobic while performing the same workout with a higher heart rate would be anaerobic.

This is where the issues get more complicated. In the short term, any activity can help build the aerobic system, even very hard efforts. But continue these kinds of exercise routines for too long and your body will break down from injury, fatigue and ill health. You’ll become a casualty of the fit but unhealthy crowd.

The one important feature that differentiates aerobic exercises from anaerobic type—in addition to lower versus higher heart rate—is time. Just because a workout stimulates the aerobic system to burn more fat doesn’t necessarily means you should keep doing it. If maintaining such a workout regularly for, let’s say two or three months, it could suddenly turn on you, reducing aerobic function, lowering fat burning, suppressing the immune system, and causing physical stress with a reduction in aerobic muscle function. Whether it takes two months, two weeks, six months or a longer time frame, this type of workout program would be an anaerobic one. Anaerobic workouts performed for weeks can temporarily build the aerobic system, but at a cost.

For a workout to be truly aerobic, you should be able to exercise the same way for many weeks and months with continued benefits. And, when you’re finished each workout, you should feel great—not tired or sore, and certainly not ready to collapse on your couch. Nor should you have cravings for sugar or other carbohydrates—your workout should program your body to burn more fat, not sugar. Burning too much sugar during a workout means it’s anaerobic, using up stored sugar (glycogen). It can even lower blood sugar. The result is that you crave sweets.

This is a key to differentiating an aerobic exercise program from an anaerobic one. While even a hard weight-lifting session can produce some of these benefits short term, it does not in the long term.

Eventually, even moderately anaerobic workouts soon can reduce fat burning and even lower the number of aerobic fibers your muscles contain. Scientists have demonstrated this fact. They have measured this decline. It’s not something based on anecdotal evidence. I have measured it too, in couch potatoes, aerobic dancers, walkers, and professional athletes.

In a laboratory or clinical setting, the process of fat burning can easily be measured with a gas analyzer – a device that assesses the air you breath. By comparing the amount of oxygen you consume from the air, and the carbon dioxide your body expires, one can determine quite accurately the amount of fat and sugar you burn. As exercise improves fat burning long term, it reflects improvements in the aerobic system. Not so with anaerobic exercise.

For most individuals, the best way to determine whether an exercise is truly building your aerobic system is to check your heart rate – following the 180-formula.

For more information on aerobic and anaerobic workouts, the relationship to food intake, and other factors, including stress, see The Big Book of Endurance Training and Racing.


  • […] of HIT. This allows for better burning of stored fat, increased endurance at faster speeds, and many health benefits. The key is to keep these types of workouts simple, short and to allow for adequate recovery time. […]

  • Girish says:

    I started MAF training only a couple of months back. But an important Half Marathon Race is coming up in three months, and I am worried that if I stick to ONLY MAF workouts, I might loose touch with speed. So, I am going for one or two HIIT/LT runs as a “cheat days” in the week, while the other 3/4 days I run strictly as per MAF HR.

    The concern is: Will my MAF/LHRT runs be “junk miles”, if I continue with a few HIIT workouts? Will these HIIT workouts hinder my base building efforts?

    For the record, there seems to be some MAF improvement in 1st mile pace of about 45 secs in pace /mile in the last 6 weeks for me. And I also find myself more relaxed, less tired, since overall my hard workout content is significantly lesser than in the past. MAF training is definitely easier on the body.

    • Hi Girish:

      They won’t be junk miles. Any MAF training helps you build the aerobic system and/or recover from anaerobic training. If you train both anaerobically and aerobically, your aerobic training will go more towards helping you recover from the anaerobic training, than towards building your aerobic base. (So it does have a real benefit, either way.)

  • Blake says:

    I checked the FAQ and the articles and the book but haven’t found an answer to this:

    We train aerobically to build a base, and this base needs to be built before doing anything anaerobic, taking any amount of time from 3-6 months (or presumably longer).

    How do we know when the base is built?

    On a related note, how do we know if we’re aerobic or anaerobic at any given moment? I mean, for real, not by heart rate calculation. One of the FAQs notes that you don’t want to spike into the anaerobic even a little bit but HR monitors (wrist monitors in particular) aren’t that accurate. And Maf notes in the book that the heart rate calculation is most useful as a starting out rule of thumb. How does one really know, then? Is a gas analyzer the only way?

    • Blake:

      The best way to know that a basic aerobic base is built is if your MAF speed has been improving for a few months. However, an elite marathoner may have been building their aerobic base over the course of decades by running hundreds of thousands of slow miles. So “building a basic base” and “strengthening a base to a certain level” are 2 different things.

      A calculation which looks at where your maximum rate of fat-burning (FAT MAX) occurs is the best way. And yes, this is done partly with a gas analyzer. To be specific, not going over an aerobic heart rate ever when you intend to do purely aerobic training is the ideal. So in that sense, insofar as you go over the MAF HR, your run will be less aerobic.

      But since you are using a different energy system, there are a whole bunch of markers that you can get to know that can help you know if you’re aerobic or not. For example, if you’re even slightly anaerobic, you should feel your breathing rate increase slightly but markedly.

  • Dan says:

    What about different sports? Most people have a lower LT and max HR with things like cycling, often 10 beats per minute less. With this 180 calculation, do you presume the same difference or do you suggest the aerobic threshold is the same across the board?

  • Francisco Tenes Lopez says:

    I have a question. Am i no sure but the carbohidrates with O2 can be burned and generate atp. Of course the trigliceridos make more atp but the combustion with O2 of glucose don’t generate láctic acid and then you could exercise during more time with gasoline (glucose) and not diesel (fat) combustible. Isn’t it.
    P.D. on the hand i believe who the metod is ok. And fabuloso. From Madrid Spain a gratefull wish of triumpht.

    • Francisco:

      Yes, but only if the body was an entirely different machine.

      For example, someone running at an easy pace will burn 800 calories an hour. Theoretically, we could keep this going forever—but again, only if the body was a very different machine. There are 2 main reasons we can’t: (1) it’s impossible for the body to ingest calories at a rate of 800 per hour while exercising—even ultrarunners who have trained this for a long time can only do 300-350, and they are burning calories at a rate of say 1500 per hour—(2) the body is wired so that at lower intensities you get more fat-burning and at higher intensities you get more sugar burning.

      So, running at a lower intensity will automatically make you burn more fats, and the only real way to burn sugar is to go to a higher intensity. But the fuel tank for sugar is very small, compared to the fuel tank for fats (2000 calories versus 55,000 in a runner with 12% body fat). So, because at a higher intensity you are also burning energy at a much higher rate, when you start to need a significant amount of sugars you may be burning energy at a rate where the sugar fuel tank will only last you 2 hours (but it takes at best 5 hours to replenish).

      Furthermore, even if it was possible to burn sugars for a long time in exercise, but not fats, you wouldn’t want to do that because of an entirely different (but related) system. The body is wired to turn all excess dietary sugars into fats. So, if sugar is your main fuel, you need to ingest a lot of sugar. And any excess sugar that you eat will automatically be turned into fats. But remember, you never trained your ability to burn fats. So you will only be able to add fats to your storage, not remove them.

      This is why there isn’t—and will never be—one single endurance athlete who owes their skill to increased sugar burning. Every endurance athlete who lives or has ever lived owes their endurance ability (their ability to exercise for a long time) to their ability to burn fats, not sugars.

      (Si prefiere, le puedo traducir a Español/Castellano).

  • Mircea Andrei Ghinea says:


    a veeery interesting article!! i read it once, and now again. i’ll come back with a few questions when things are more clear to me so i’ll know better what to ask.

    i see that Ivan Rivera reply here. is Phil Maffetone reading our questions/comments or not? is the answer coming from Phil or from Ivan?

    thank you!

  • James says:

    Hi Ivan,
    I used to do road cycling before I got into running, climbing. This was a long time ago – 5-8 years. I just got a new mountain bike. First ride today, with the HR monitor on. I only did 35 minutes however my MAHR of 154 is crazy hard on a bike compared to running, my quads felt really heavy with lactic at this HR when climbing a hill, my breathing felt OK though. When running at the same or slightly lower HR it feels like a comfortable cruising effort. I didn’t warm up enough today and I was concentrating on traffic and learning the handling of the bike but my HR shot up a lot quicker than when I run or cross train on the eliptical/rowing machine. Didn’t feel ‘refreshed’ at the end like I usually do after a MAF workout.
    Any thoughts?

    • Not a big deal. There’s a big difference between a bit of anaerobic activity/stress here and there and going out and doing bike intervals every day. Learn the skill, and learn the road, and focus on that, and do what you can with your heart rate.

      • James says:

        Thanks, the perceived effort felt off the scale higher than it did for running at the same HR. I guess the road surface, traffic, controlling the bike etc is going to have an affect on your HR compared to running where you can (comparatively) just cruise along without a great deal of thought.

        • James:

          Generally speaking, yeah. The relationship between stress and anaerobic function is bidirectional: if I make you train anaerobically I’ll increase your stress levels, but if I come up behind you and scream into your ear, I’ll also put you into anaerobic function (as your body prepares to escape from a threat). Attention itself (even when you’re talking about attention to your HR) counts as stress, albeit small.

  • umesh says:

    1) Does that mean we should not call Aerobic exercise as cardio ? Because people think anything that increases your heart rate is Aerobic.
    2) If anyone wants to reduce fat in the body and given a choice of running versus brisk walk, then which one should be followed?
    3) When people think more sweating (indirectly more heart rate) means faster fat loss, is it true or false?
    Thanks for your time..

    • Umesh:

      Thanks for commenting. Let me answer your questions in order.

      1) That’s exactly right.

      2) It depends. “Running” at a good speed can be totally aerobic for someone, and totally anaerobic for someone else. It depends on how developed their aerobic system is. (For example, an elite marathoner may be doing 5:30 minute miles at a pace that is almost completely aerobic. Not so for the rest of us.) Walking is therefore a much surer bet that you are going to be burning fats.

      3) False. Sweating itself says nothing about whether you are burning fats, and doesn’t make you burn fats. You might lose weight, but that’s because you lost water. But I think there’s a little more packed into your question: While high-intensity training (a higher heart rate) can make you lose fats fast, the problem is that too much of this means a level of stress that causes your body to stop burning fats and instead burn sugar, which means that you rebound and gain even more fats. So the answer to the question of “how to lose fats the fastest” is “by keeping them off well.”

  • C says:

    I am not sure if my previous comment went through as my webpage froze so I’ll try to rewrite it.

    Hi Ivan,

    I am scheduled to attend a Spiroergometry (respiratory measurement with exercise ECG) tomorrow morning. One of the key findings from this test would be to get accurate readings of my RQ levels. I wanted to make sure that the findings of the RQ somehow can translate to an even more accurate MAF HR (is that possible?). I have tried to read up more on RQ in the Endurance book and refer to the section with Mike Pigg. I have to admit that it is not entirely clear to me how to interpret it. It sounds like at even at really low HR he was still burning significant amount of sugar (30%) and not sure that is really optimized?

    Is the RQ=0.85 = 50/50 sugar/fat = 50/50 aerobic/anaerobic = MAF optimized HR? Please correct what is wrong in this equation.

    My key question is still how can I use the findings of the test to optimize the benefits of the MAF training concept?

    Thanks again for your devotion to this forum!

    Kind regards,


    • C:

      Sorry; I’ve been busy with a lot of different projects and haven’t gotten to the website comments. I usually have a lag of 2-3 days, as I let them build up. An RQ of .85 typically matches up quite well with the MAF heart rate. However, look at your MAF heart rate and see if there is a discrepancy with the heart rate at which you get a .85 RQ.

  • C says:

    Hi Ivan,

    Thanks for your previous response regarding heat and impact on HR in another article.

    I now have a question which actually might be more of a clarification. This article talks about the difference between aerobic and anaerobic exercise but I feel that there is some confusion regarding the terminology based on my own experience. You have concluded that all endurance racing and endurance traning for that matter by definition is regarded to be AEROBIC. In particular Ironman which is what I am referring to. When I am/was racing Ironman my HR used to average 160bpm for say 9.5h which according to your definition is AEROBIC. When I am now MAFing to get my health back I am at 135bpm limit which is clearly also AEROBIC.

    Question is why is suddenly my HR when racing IM ANAEROBIC when I refer to my MAF but AEROBIC according to your statement that all endurance events are 100% AEROBIC? Maybe the answer lies in the fact that despite being labeled as AEROBIC at 160bpm the proportion of sugar vs fat for energy transportation is to the benefit of sugar? By what margin we don’t know but in my view, in order to differentiate between AEROBIC and ANAERBIC, we should say that as soon as the scale tips from being 50/50 (assumed MAF target level) to 49.9% fat and 51.1% sugar we are ANAEROBIC. Does that make sense?



    • C:

      Yeah. That’s a pretty good rationale. Sometimes it’s tough to keep track of all the ways that I use the words “aerobic” and “anaerobic.” Wha”t I meant by using the word “anaerobic in the discussion on racing is not that racing is anaerobic per se, but rather that, if you’re going to use the anaerobic system, then do it while racing, not training. (For example, running hills during an endurance race will typically make your effort anaerobic for that time).

      In other words, by saying that “training is aerobic, racing is anaerobic” what I really meant is “train anaerobically minimally, race anaerobically when the event requires it.”

      I hope this clears it up.

  • Gary says:

    In Phil’s big book of health and fitness, he mentions a gas analyzer to determine the amount of fat vs. sugar burned. Will you recommend a brand or website for me to further learn and use in my practice?
    Dr. Gary

  • Maria says:

    Thank you for the reply to my query. Your reply has cleared up the confusion. I do some HIIT workouts but only when I am short on time. From your reply it seems that I am doing something right. Now if I could keep my heart rate at the MAF level?
    Thanks again

  • Elaine Hellmann says:

    Just started

    • Maria says:

      Hi. Lately we are hearing more and more about HIIT and that it burns more fat than aerobic training but as an after effect and for a longer period of time.
      As an athlete who would like to remain lean for my sport, this gets very confusing. I am a long distance runner and I realize that distance is important. I am also reading that the LSD does not burn the fat at the same intensity as HIIT.
      Can you offer some feedback?
      Thanks Maria

      • Maria:

        Great question. This is actually going on the FAQ list we’re currently building. But let me answer it for you now.

        HIIT burns more fat than LSD because it burns an immense amount of energy in a very compressed time frame. But percentage wise, LSD burns much more fat than HIIT does. The problem is that HIIT (anaerobic exercise) breaks the body down, which is why you see so many crossfitters with overuse injuries, exertional rhabdomyolysis, or brittle bones–like when my brother, a lifelong martial artist, broke a bodybuilder’s forearm bones while arm-wrestling.

        The body was never meant to exercise that much, that intensely, without a very powerful aerobic base beneath it. When you have a very powerful aerobic base, the amount of total calories (and fat calories in particular) that you can burn dwarfs the amount of calories you could burn in HIIT.

        So it’s not really about fat, and it’s not really about whether LSD can go toe to toe with HIIT in a calorie-burning competition: it’s about developing that aerobic base that thenallows you to endure anaerobic workouts and the development of type I muscle fibers without the adverse health effects. With that aerobic base, the amount of fat that you can burn (and the overall training volume your body can endure while staying healthy) is massive.

        This is why at MAF we don’t advocate for any kind of long slow distance. We advocate for the majority of exercise being at a particular heart rate: the MAF heart rate, or rather, the one that maximally develops the aerobic system, which means the lungs and alveoli, capillary networks in the muscles, Type I fibers and their mitochondria, and of course, all the neurological and endocrine underpinnings. This system helps the anaerobic Type II fibers (the kind you train during HIIT) process excess lactate, and so on and so on.

        To use a metaphor, imagine that anaerobic exercise is like playing jenga. You can build up the tower and make it taller, but at some point you’re going to be taking away from the foundational building blocks that keep that tower upright. By training the aerobic system, you increase the amount of blocks at the base, that you can then take from, with more anaerobic workouts, and make your tower taller. And we can take this a little further: just like in the metaphor, any time that you add power to your anaerobic system, it comes at the cost of your aerobic system.

        Let me end on this note: you need both systems to be a well-rounded athlete, but the aerobic system is without question the foundation on which the anaerobic system can be built. Our modern approach to sports neglects this, and this neglect is one of the primary contributors to the present injury rates we see.

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