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 on their red blood cell. 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!


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. 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 :)

Leave A Reply