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John Cardillo: Understanding Aerobic Energy Vs Anaerobic Energy

Look around any fitness centre these days and you will see the cardio machine area jammed with people running on treadmills, using stepper machine or giving a rowing machine a workout. With the primary purpose of shedding unwanted adipose fat and improving the cardiovascular health.

When I see these dedicated workout enthusiasts I always wonder if they know what they are doing? Are they on a set cardio program? Do they know what intensity level they need to be working at, or where their heart rate needs to climb to for their bodies to even start burning their unsightly badyfat? Some may know.

Based on my years of experience I know for a fact that most don’t exactly understand what their maximum heart rate fat burning zone is. In this article I want to explain in detail how a person should perform cardiovascular exercise to achieve meaningful fat loss.

Aerobic Versus Anaerobic Exercise

The meaning of Aerobic exercise is the performance of low to medium intensity exercise over a longer period of time using oxygen and fats as fuel.

The meaning of Anaerobic is the performance of hi-intensity exercise over a short period of time using muscle glycogen for fuel.

The Science of Fat Metabolism

The science of getting into your fat burning zone is dependent on exercise intensity to increase heart rate and increase oxygen uptake, referred to as VO2max. VO2max is simply the maximum amount of oxygen that you can consume to keep up with your metabolic demands. The harder and longer you work the more oxygen you are going to need. Gaging your heart rate is also fairly simple, the harder you work the faster your heart is going to pump in order to keep up with demands. Your maximum heart rate formula is defined as 220 minus your age. Therefore a 40 year old male’s maximum aerobic heart rate will be 180 beats per minute. However, that still is not the optimal heart rate and oxygen consumption to burn body fat. Let’s look at the various fat burning states:

  1. In a fasted state, fat is going to be the predominant fuel source when doing daily low intensity daily tasks/activities. This means that your body is operating at 35% of VO2max (180x .35= 63 beats per minute). During this phase your body is using primarily free fatty acids (FFAs) that are found in the blood stream or from fat cells, for energy.
  2. As intensity increases due to medium exercise exertion, to 65% VO2max, your heart rate will increase (180x .65= 117 beats per minute). Your body will continue to use remaining FFAs in your blood stream for energy. Once your bloodstream FFAs are depleted, your body will summon the hormone Glucagon to act on your fat cells to release more fatty acids for energy. This is where the bodyfat burning zone starts.
  3. In my experience 65% to 75% of my VO2max zone was the sweet spot for burning the most bodyfat. This meant that the aerobic exercise which I was doing caused my heart rate to increase to between 119 to 125 beats per minute, which forced my body to consume oxygen at a fairly high rate. Meaning that I was breathing heavy but not gasping for air.
  4. The metabolic process whereby fatty acids that have been released from the body’s adipose fat storage enter the muscle cell through the cell membrane, to be broken down and used for aerobic energy. This is called beta oxidation (slow glycolysis). Which is a process that takes place in the muscle cell’s mitochondria. The fatty acids first get broken down into acetyl CoA. Here the acetyl-CoA goes to the muscle cells Krebs cycle, and then through a process which produces ATP for energy needed to fuel your body’s aerobic activity.

Aerobic vs Anaerobic Energy Source

One of the main reasons for our bodies burning stored bodyfat from our adipose cells during aerobic, medium intensity exercise, is due to the muscles being used not contracting to their maximum ability, as they would when performing hi-intensity anaerobic weight exercise. When a muscle is being exercised anaerobically, with extreme hi-intensity, your heart rate will increase to more than 50% higher than your VO2max, forcing the muscles being used (contracted) to draw on stored glycogen for energy. As such, intensity is the predictor of which energy source your body uses for energy. Our bodies are efficient in using different energy sources for different intensities of tasks.

If we were to increase our aerobic workout intensity to 85% VO2max, where our heart rate would increase to 153 beats per minute, your body would need to start to draw on muscle glycogen for energy to accommodate the higher muscular intensity being performed. At this higher intensity your body is going to use 1/3 fat for energy and 2/3 stored glycogen (carbohydrates). By increasing the intensity of any exercise you will see a decrease in the duration of performing the exercise. Because a muscle’s glycogen storage is limited, to fuel hi-intensity anaerobic work. While fat is not an efficient fuel source for hi-intensity anaerobic exercise.


  1. To burn the most amount of bodyfat, aerobic exercise should always be performed in a faster state.
  2. To calculate your optimal fat burning zone the most reliable formula (VO2max) calculation is: 220 less your age (40) =180 x 70% = 126 beats per minute
  3. Aerobic exercise should be performed at least 3 days per week for 30 to 45 minutes
  4. Never allow your heart rate to rise higher than 70% of your VO2max so that you are only using body fat for energy and you do not deplete your muscle glycogen, which is needed for anaerobic hi-intensity workouts.
  5. To avoid overtraining never do aerobic and anaerobic workouts on the same day.
  6. Aerobic exercise should be of a low intensity nature and enjoyable. There’s no need to be overly aggressive when performing aerobic exercise. Being overly aggressive will transform the exercise from aerobic to anaerobic

This guest post was submitted by John Cardillo.