Biggest Workout Mistake – Aerobic vs Anaerobic Workouts


Of all the different workout mistakes, probably the one that slows down your results the most is performing aerobic exercise in an anaerobic state. Simply put, doing your aerobic exercise at too high of an intensity for your current fitness level.

It’s easy to think that just because you are doing an aerobic exercise, that it is aerobic. That’s not necessarily the case. You could be performing your aerobic activity at such an intensity, that it becomes anaerobic and stress producing on your body.

The determining factor whether your body is triggering aerobic or anaerobic metabolism is the availability of oxygen. If there is oxygen available, your body will generate energy by aerobic metabolism. If there is only a limited amount of oxygen available, because you are breathing hard and panting, your body will produce energy through anaerobic metabolism.

Think of these two systems like a hybrid car. It can produce energy if there is or isn’t oxygen available. If there is oxygen, you burn fats. If there is no oxygen, you burn carbs and lean muscle.

Both aerobic and anaerobic metabolism will provide energy for your workout. The difference or limiting factor is oxygen. An abundance of oxygen will trigger aerobic metabolism and breakdown fats for energy. This is what most people are after if they are trying to lose weight and keep it off. Anaerobic metabolism breaks down carbohydrates and proteins (lean muscles) for energy, because there is only a limited amount of oxygen available.

The biggest downside to this training mistake is that it can quickly slow your fitness progress and lead to overtraining, fatigue, adrenal exhaustion, or hormonal imbalances. Keep in mind that true aerobic exercise is stress reducing, whereas anaerobic exercise is stress producing.

Rule of Thumb
biggest-workout-mistake-cardio-1When you finish your aerobic workout, ask yourself a question. Can you do the exact same aerobic workout again? Basically, can you do a back-to-back aerobic workout? If you can answer yes, you’re probably training aerobically. If your answer is “are you insane, that will kill me” that may be a tip-off that your aerobic workout is too intense for your current fitness level and you need to slow it down.

A lot of people like to perform one day of hard intense anaerobic training and balance it out with an easy aerobic workout. That’s a good thing since it allows your body time to recover so your growth hormones and testosterone can be released and utilized. However, if your aerobic workout is triggering anaerobic metabolism, you could be performing 100% of your workouts anaerobically!

That’s not a good thing and you’re not giving your body any easy days to recover and rebuild those muscles you tore down. What you are doing is constantly pushing and punishing your body with these intense workouts and your body may not be able to handle all the additional physical stress you are throwing on it. Not to mention all the other mental stresses you are placing on your adrenal glands, the organs responsible for producing your stress hormones, cortisol and adrenaline.

The Types of Workouts
Aerobic exercise is anything you can do for a long period of time at low to moderate intensity such as walking, jogging, cycling, etc. The fact that it is low to moderate intensity allows your body to supply adequate amounts of oxygen to your muscles for fuel.

Anaerobic exercise is essentially the opposite. It is short duration, for moderate to high intensity. Because the workout is more intense, the body has a limited amount of oxygen available and will breakdown carbohydrates and proteins (lean muscle) for fuel, instead of stored body fat. Classic anaerobic exercise is weight training, sprinting, downhill skiing, 1-3 minutes of boxing, etc.

Finding Your Aerobic Zone
What determines your aerobic or fat burning zone is your heart rate. For most people, keeping your heart rate between 60-85% of your maximum heart rate will keep you in your fat burning zone. The problem for the most part is our ego. Some people who may be 20-40 plus pounds overweight and they are training as they did when they were 20 years old. You can’t do that since everyone is at different fitness levels and some of us need to keep our fat burning zone at 65%, others can train at 75%, and the elite conditioned individual can perform cardio at 80-85% of their maximum heart rate.

Essentially, the only people who can train at 80% of their heart rate and still be aerobic and burning fats are your “well-conditioned” marathoners, tri-athletes and cyclists. Unless you are one of those individuals who are charting 50-150 miles a week on the pavement or bike, you should keep your heart rate at no more than 70-75% of your maximum heart rate. Remember, aerobic exercise should be low intensity, stress reducing and something you can do for a long period of time.

Many times, I’ll see two people jogging or walking on the road together who have two different physiques. Depending on the speed they are going one person may be getting true aerobic conditioning, while the other is triggering anaerobic metabolism.

Simple Suggestion
biggest-workout-mistake-cardio-2Use a heart rate monitor when you perform your aerobic exercises. Keep your heart rate at 70% of your maximum heart rate. To find your maximum heart rate subtract your age from 220. That will give you your maximum heart rate. Next multiple it by (.70), to find 70% of your max heart rate. A 40-year-old individual would be (220 – 40 = 180) multiplied by (.70) gives us 70% of his maximum heart rate, which equates to 126 beats per minute.

Now go out and run, jog or walk outside but do not use a treadmill for this test. See if you can keep your heart rate at or below your Target Heart Rate. Most of the people I suggest this test for, come back and say, I pretty much had to walk to keep my heart rate at or below that level. If that’s you, that’s a good sign that your aerobic capacity is not where you think it is and your workouts are probably working against you.

I also suggest you perform your normal aerobic workout at your normal speed and intensity. Check to see what your heart rate is for that workout. A lot of people come back and say, I had no idea I was performing my aerobic workout at 80-90% of my maximum heart rate, what a mistake! That probably explains why they feel the way they do.

Food For Thought
If your heart muscle is pumping at 70-75% of its maximum and your legs are pumping at only 20-25% of the maximum speed you can run, do you think your aerobic conditioning needs some adjusting? Don’t measure your level of fitness by how little body fat or how much muscle you have. Your aerobic conditioning is all about how much oxygen each one of your red blood cells can carry.

The reason well conditioned runners and cyclists have such low resting heart rates is because their red blood cells are carrying a lot of oxygen. Their oxygen capacity is much higher. The less conditioned individual can’t carry as much oxygen in their red blood cells. Their aerobic capacity is less. Thus their heart has to beat faster in order to send an equal amount of oxygen to your muscles.

Your anaerobic workout should be as intense as you want to make it. It is your aerobic, cardio workout we’re talking about. When you stay aerobic, this is when you get all the cardiovascular benefits for your heart. This is where you expand your aerobic capacity. This is where many of your elite runners and cyclist spend most of their off-season, expanding their aerobic base with long, low intensity workouts.

Again, only the well conditioned and elite runners and cyclists can keep their heart rate between 80-85% of their max heart rate and still be aerobic. Unless that’s you, keep it around 65-75% of your max heart rate. If you’re overweight or haven’t been working out too much, you should stay closer to the 65% mark. Don’t let your ego get in the way as it did for me years ago. It’s what made me want to only run at night so no one would see how slow I was running.

True aerobic exercise should be nice and easy! Don’t make this common mistake and overtrain your body. If you’ve hit a plateau, can’t figure out why your results have stalled or why you are constantly tired and fatigued after a workout, then take a closer look at your aerobic intensity? Maybe adjusting the intensity is all you need to help your body recover and repair itself. I don’t know about you but most people don’t have the time and energy to be wasting!

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About Author

Dr. Len Lopez

Dr. Len Lopez is a nutrition and fitness expert. An athlete and fitness enthusiasts all his life, his background in sports medicine, nutrition and fitness training gives him insight to help those who are struggling with both their health and fitness levels. See my profile page for more information!


  1. Avatar

    Why is there no consistency of opinion in the fitness world? I have read several articles that say anaerobic exercise is better than aerobic. My husband yells at me at the gym for getting my heart rate above 130, but I don’t FEEL like I’m working out if I’m not sweating and really breathing hard. I wish someone could just declare who is right so that I can move on with my life and not wonder about this phenomenon over and over 🙂

    • shapefit

      Kate – I think the answer is that there really is no definite “right” answer since each person’s body, metabolism and genetics are different. It comes down to what works best for you in terms of losing body fat and maintaining lean muscle mass while doing cardio exercise. There is a lot of evidence that HIIT (high intensity interval training) works the best for losing fat but some of the things to be aware of include the overtraining issues and safety concerns (injuries) this type of training could possibly cause if performed too much. HIIT produces that “afterburn” effect which is also known as EPOC (excess post-exercise oxygen consumption) where you burn calories for several hours post-workout. The other side of the coin is the “steady state” cardio folks (like your husband) who think you should stay in your fat burning zone throughout each cardio workout. Any intensity level above this low intensity zone and you will be burning carbs (sugar burning) instead of fat burning. I highly recommend trying both methods for 3-4 weeks and make sure to take photos along the way to document the changes in fat loss and overall muscle tone. A lot of people also like to mix it up and include 1-2 days of HIIT training per week along with their “steady state” cardio workouts. Best of luck to you 🙂

  2. Avatar

    I’m a long time runner now in my mid 50’s. I’ve run numerous marathons and ultra marathons in the last 10 years. However, a few years ago I lost my stamina and interest in endurance training and events. I have kept my running routine between 5-8 miles 5 days a week for a total mileage per week of around 25-30 miles. Once a week I include 4-6 one minute intervals with a one minute recovery but otherwise I run “easy”. But it never feels easy anymore. It feels like I’m exerting enough effort that I want the run to be over. My husband recently bought me a new watch with a heart rate monitor and I found that on an “easy” 5-8 mile run my heart rate was always in the threshold or higher range (145-155). Based on the 220 formula my aerobic HR is 116 and according to the Maffetone method aerobic zone is 115-125. So this would suggest that all my runs for numerous years have been in a stressed state. My blood pressure is good/low at 90/60 and resting pulse is 53 so all that would seem to be in accordance with good cardio fitness but my aerobic capacity is not good because my runs feel draining even at the 9-10 minute mark. If I switch to an aerobic zone pace to build aerobic fitness, what duration should the runs be and about how long will it take to see improvement? I really want to start loving to run again!

    • shapefit

      Hi Dawn – Did anything happen in the last few years that could have affected your overall stamina and interest in running like a loss of a loved one, excess work stress or health issues? Many times, extra stress from outside sources can cause issues to one’s overall health and even though it may not be seen as being really “stressed out”, these small things can slowly creep up on you and cause problems.

  3. Avatar

    Hi ShapeFit! I started running in mid-2012 (I was 17 then). I used to run 3-8 miles without much planning. Basically, the distance I ran depended on how I felt on a particular day and I didn’t follow a pattern as such and also took random rest days when I felt I needed it. Most of it was anaerobic running. I experienced constipation beginning in late 2012 and ran my first half marathon (finished in 2:10) in April 2013 in spite of the constipation problem after which it worsened. I stopped running in August 2013. Three years later, the ailment persists even though I don’t exercise at all. The problem is very strange (plus embarrassing) since we all know that if anything I should be having diarrhea. I have always had good fiber and water intake so the problem is not caused by the lack of either of the two. I think, most likely, it arose because of irregular, anaerobic running and adding distance quickly. What do you think?

    • shapefit

      Hi Prateek – That’s a very interesting question and we are at a loss as to what could be causing your constipation. Have you been able to visit your doctor to do a full checkup and see what they think might be happening? It might have nothing to do with your diet and could possibly be a stomach issue that would need to be addressed by a physician. It’s probably best to be on the safe side and make an appointment soon 🙂

  4. Avatar

    I’m 22 years old and I’m trying to be a soccer player. I’ve read your article and I found it very informative and simple. I would like to thank you for that. I have a dilemma in terms of expanding my aerobic levels because soccer is an aerobic/anaerobic sport (a professional soccer player runs around 10 km in 90 minutes). My question is if my aerobic zone is at 60%, how can someone reach to 80% and expand their aerobic level without risking performing my workout anaerobically? My recent training results are: 3 km in 20 minutes (HIIT Training), 3 km in 30 minutes (slow and steady run). After I read this article, I can assure you that this run wasn’t aerobically focuses like I intended. I’m following a 10k program that covers 16 weeks. It includes slow runs, interval training, Tabata, tempo runs, etc. If you have any advice on how a soccer player can increase his aerobic and anaerobic levels that would be great. Thanks in advance and keep up the great work!

    • ShapeFit

      Hi Omar – To increase your aerobic level, it will take a lot of trial and error on your part by testing different training routines. You can start with increasing your HIIT training to 30 minutes and your slow cardio training to 40 minutes. Do this for 2-3 weeks and see how you feel when you’re on the soccer field. Each person’s aerobic level is different so you will need to see what your “sweet spot” is during many different training routines. The end result will be how you perform on the soccer field so keep tweaking your training until you get the best results. Good luck!

  5. Avatar

    I am a 44 year old male and my max heart rate is 176. 70% of that is 130. Getting my heart rate to this number is a simple leisurely stroll. I have seen other charts that list my target heart rate at 144 (70%) for my age. Why is there no consensus about this? At 130, I don’t feel like I am doing anything. I am trying to lose weight while building muscle. I do a combo of weights, steady state cardio and intervals.

    • ShapeFit

      Hi Eric – Your target heart rate should be a general guideline when exercising since every person is different. It really depends on your overall level of fitness. You are probably in better shape than most 40-year-old individuals, so even though working out at a heart rate of 130 seems easy for you, it might be much more difficult for others. Try to go by how you feel and use your heart rate as a secondary input to your workouts. If you’re barely breaking a sweat, then kick it up a notch. On the other hand, if you can barely catch your breath then decrease the intensity. It’s more about “feeling” your workouts and this goes for both cardio exercise along with weight training workouts. If you don’t “feel” your muscles working with a specific exercise, then try a different one and see if it engages your muscles better. Achieving the physique you want is a lot about trial and error, and you need to “tweak” your workouts in order to completely dial in your training to produce the best results for your own body.

  6. Avatar

    I’m 22 years old and I go to the gym twice a week. My routine is doing anaerobic (weight lifting) exercises for about 30 minutes after a 10 minute warm-up and then I do cardio after on the treadmill for about 20 minutes. While on the treadmill, I usually run to the point where it is aerobic. I haven’t seen any changes in muscle mass since I’m working against myself. I’m wondering if I should change my routine to a day of anaerobic training and then the other day I would just jog at a descent pace on a treadmill or bicycle. Do you think this routine will work or do you have a better idea?

    • ShapeFit

      Hi Jose – Yes, you could try separating your weight lifting workouts from your cardio training days and see how that works. You should also focus on your total calories consumed and make sure you’re eating enough to spur growth. There are many factors when it comes to gaining lean muscle mass, so it’s important to hit it from all angles.

  7. Avatar

    I am 71 years old, 6’3″ and 225 lbs, i.e. about 25 lbs overweight. My resting rate is 62 and I have been somewhat active, but I decided two months ago to take a serious effort to improve my cardio fitness, improve my overall fitness, and lose a some weight as I progressed. I bought a heart monitor watch and a chest strap and dusted off our exercise equipment which has pistons to create resistance to strengthen the upper body. My maximum heart rate is 149 (220-71) and my target heart rate is about 105 bpm (70% of 149). I now warm up for three minutes and keep my heart rate between 105 and 108 for an hour per day, first thing in the morning, 5-6 days per week. I can still talk and whistle and sing a little at the end and feel like I could keep going. What do I need to change?

    • ShapeFit

      Hi Fred – It sounds like you are on the right path and don’t really need to change anything at all! Great job staying active at your age and we wish you the best reaching all of your fitness goals!

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