Aerobic vs anaerobic for fat loss, which is better? The answer – both. Fat has more energy (calories) per gram than carbohydrates but it takes the body longer to use it. We want to burn those calories, but how does the body go about it?
Aerobic means ‘with oxygen’ and is the type of repetitive exercise that is done at low to intermediate intensity. Often referred to as steady-state cardio. Running, cycling and swimming can all be types of aerobic exercise (depending on intensity) and generally used to build endurance. Your heart rate will be somewhere between 50-80% of your maximum heart rate, MHR, and covers quite a range of target zones. Oxygen is the main source of fuel for the body. This type of exercise can be done, potentially, for hours.
Anaerobic means ‘without oxygen’ and is where the body requires immediate energy, using glucose, in the form of carbohydrates and sugars. This is done in shorter higher intensity bursts to build muscle strength and power. Think sprinting, jumping, HIIT workouts and strength training. Here your heart rate will often be above 80% of your MRH, but this can only be maintained for short periods of time (could be as short as 10 seconds or as long as 20 minutes, it depends on how close to your max heart rate you are, your intensity, and how you feel. Your perceived exertion)
The difference between aerobic and anaerobic is when your body can not take in enough oxygen, quickly enough, to fuel the muscles. When it can it is aerobic exercise, when it cant its anaerobic. As an approximate guideline, it will be when you can’t hold a conversation easily without having to stop for breath between words or sentences and your breathing becomes harder.
Max Heart Rate (MHR) & Target Zones
There have been changes to this in recent years, particularly with regard to women. Historically, to calculate your maximum heart rate you subtract your age from 220.
For example, if you are 40 years old your maximum heart rate will be: 220 – 40 = 180 beats per minute. This generally works out about right for men and isn’t a bad target. (There are other formulas like the: 207 x (age x 0.7) for people over 40 or for fitter individuals using 211 – (age x 0.64) Remember these are all generic figures and you can get above these)
For women, recent studies show that their maximum is slightly less than men: A newer formula gives: 206 – (age x0.88)
So for a 40 year old woman, her maximum heart rate would be 206 – (40 x 0.88) = 171bpm instead of 180bpm for a man.
Once you know your MHR you can work out your target zones. This is where aerobic and anaerobic come in.
Target zones are where the body is exercising within a certain range of MHR.
For example, if you wanted to exercise at 70% MHR and see if it was aerobic or anaerobic for you, or for how long you could train like this before it became anaerobic. To get your target zone you need your HRR, your Heart Rate Reserve.
HRH is calculated by subtracting your resting heart rate from your max heart rate. (Take your resting heart as you are lying in bed in the morning, or while you have a few minutes just sitting doing nothing). For most people, a resting heart rate will be anywhere between 40 and 80.
If we take our 40 yr old man:
- Max heart rate: 220 – 40 = 180bpm
- Resting heart rate of 60bpm
- HRH: 180 – 60 = 120
- Target is the 70% zone
- 0.7 x 120 = 84
- Add this to his resting heart rate: 84 + 60 = 144bpm is his target heart rate to work in the 70% zone
- For the 80% zone it would be: 156bpm
For our 40 yr old woman (using the updated formula):
- Max heart rate: 206 – (40 x 0.88) = 171bpm
- Resting heart rate of 60bpm
- HRH: 171 – 60 = 111bpm
- Target is the 70% zone
- 0.7 x 111 = 78 (77.7)
- Add to her resting heart rate: 78 + 60 = 138bpm is her target for the 70% zone
- For the 80% zone it would be: 148bpm
Nowadays there are lots of health accessories and apps to help you find all of this data. Your watch or heart rate monitors are an excellent place to start and will give you valuable information. Others will even be able to tell you when it’s the best time to train or whether not to train.
Before we get into the target zones we’ll discuss perceived feeling in exercise. Perceived Exertion (Borg rating: Rate of Perceived Exertion, RPE) is based around how a person feels while doing an exercise. How hard they feel they are working. It is based on factors like heart rate, breathing rate, muscle fatigue and sweating. It is linked to your heart rate and can give a good idea of what zone you are in. For example, if you are unable to talk while exercising you would be working towards the higher intensity levels.
The target zones:
Target zones are intensity regions and used to improve a particular aspect of fitness or weight loss. They are used to set specific intensities in which to complete an exercise. Generally, these are split into several different categories and there isn’t one that covers them all. The easiest to understand is the three-zone model (however there are some that use up to seven zones if you want to get very particular) The three-zone model is based on perceived exertion:
- Zone 1: Easy exercise, around 50-65% MHR, where you can hold a conversation easily and can sustain the exercise without any difficulty. Breathing is easy.
- Zone 2: More difficult exercise, 60-80% MHR, where you can speak but have to take breaths between words or sentences, difficult to hold a conversation as your breathing becomes more difficult.
- Zone 3: Intense exercise, 80% plus, breathing is hard, words are very difficult and you can not keep this up for a long period of time.
- Between zones one and two will be the Aerobic zone where the body will burn more fat than glucose. Like this the body can potentially go on for several hours.
- Between zones two and three will be the Anaerobic zone where the body will burn more glucose. Here the body will not be able to cope and your exertion levels and heart rate will continue to rise until you can not continue.
This model is quite good if you don’t have any sort of heart rate monitor for gauging what your heart rate might be. We can assume for our healthy 40yr old man that if he is running, breathing is relatively hard and only one sentence at a time can be spoken before several breaths need to be taken; then he is more than likely in zone 2 and on the Aerobic Anaerobic threshold.
A 5 zone model will be expressed as something similar to this.
- Low intensity: 55-65%
- Moderate intensity: 65-75%
- Aerobic zone: 70-80%
- Anaerobic/vigorous intensity: 75%-95%
- Maximum intensity: 95% +
5 zones and above are geared more towards the serious athlete who wants to target a certain improvement. Keen/top cyclists will be an example of this.
Why we can’t maintain Anaerobic exercise for long periods
When we exercise hard we use oxygen to break down glucose for energy, anaerobic exercise. As you work harder your body can’t take in enough oxygen quickly enough to keep this process up. When it can no longer do this it produces lactate (lactic acid). Your body can convert this lactate to energy without the use of oxygen. However, the lactate can also build up in your bloodstream more quickly than the body can burn it off (this point is called the lactate threshold). Once you get to this point there are several symptoms you may experience. It’ll often start with a burning feeling in your muscles, leading to cramping, weakness and possibly nausea. At these points, you simply can’t continue.
Aerobic vs Anaerobic
Now we know that aerobic is a more low-intensity workout, using oxygen as its fuel and anaerobic is a higher intensity workout, using glucose from sugars and carbohydrates. Which one actually burns more fat.
For any exercise, it will take the body longer to convert fat into energy than it will carbohydrates and sugars (carbs)
However, fat has more energy, or calories, per gram than those in carbs. In fact, fat has more than twice as many calories per gram than carbohydrates.
- Fat: 9 calories per gram
- Carbohydrates: 4 calories per gram
Your body will use some or all of the carbohydrates for fuel first depending on how hard you are exercising and for how long. After it will start on the fat reserves. So, how much fat you burn will depend on how hard you are working and for what duration.
Aerobic exercises will use more sources of energy than anaerobic and will therefore burn more fat but requires less energy. If less energy is required, fewer calories are burnt off.
Anaerobic exercise will burn more calories than aerobic but can’t be performed for as long.
Looking at the numbers:
- Aerobic exercise uses around 60% of calories from fat reserves
- Anaerobic exercise uses around 35% of calories from fat reserves
From this, you would think that aerobic is the better exercise to burn fat. However, we have to look at the total number of calories burned for the same time duration.
In a 30 minute, low intensity, aerobic exercise, where you burn 200 calories, 60% will come from fat. 60% of 200 = 120 total calories from fat.
For the same 30 minutes exercising at high intensity, anaerobic exercise, where you burn 400 calories, 35% will come from fat. 35% of 400 = 140 total calories from fat.
This example shows that overall anaerobic will burn more fat for this particular scenario. However, we know that this can not be sustained and we will have to slow down back into the aerobic exercise afterwards.
Because of these findings over the recent years, there has been a big increase in the number of HIIT (High-Intensity Interval Training) workouts that incorporate aerobic, anaerobic and strength or resistance training. The anaerobic part will burn off the glucose stores, durning the rest periods your heart rate is down in the aerobic range, allowing your body to get the required oxygen and the strength training for building muscle which helps increase your metabolic rate and burn more calories while at rest throughout the day.
Another reason these type of classes are popular is because they don’t take up a lot of time. Often less than an hour and because they cause the ‘afterburn’ effect.
The afterburn effect or the Excessive Post-Oxygen Consumption (EPOC) is where the body needs to replace the lost oxygen to recover after exercise. Because anaerobic exercise uses more oxygen it takes longer to recover to its resting state and hence keeps on burning the calories even after your workout has finished.
All of this being said, aerobic exercise is just as important because it builds up endurance, however, in the modern world, people don’t seem to have the time to do longer periods of exercise.
- Ultimately, the longer you exercise, the more calories you will burn and therefore more fat.
- Anaerobic exercise will burn more calories than aerobic exercise in the same amount of time.
- Aerobic exercise will use more fat as fuel. Anaerobic more glucose.
- Both are required to help in fat loss.
- The quickest way for fat loss is by mixing both (as long as you have a sensible balanced diet)
- A example of using both (if you have the time):
- A strength training workout for 20-30 minutes to use up the glucose stores.
- Followed by a steady state aerobic exercise like running, cycling, swimming etc.. for approximately an hour, so the body will be using up fat reserves.
- And finishing off with a high intensity interval training exercise to increase the heart rate again and boost the EPOC effect. For example, interval training on a rowing machine for 5 to 10 minutes.