Fitness  – Aerobic and Anaerobic

I have been asked about this question a few times, and the answer is always, well it depends… let me explain why.

A small amount of science.

Adenosine Triphosphate (ATP), is our energy molecule and is found in every living cell. Our metabolic systems use ATP in order to create energy, muscle contraction, transmission of nerve impulses amongst many other energy consuming reactions. It is our energy currency.

• ATP energy is obtained by the breakdown of food.
• We can breakdown EITHER carbohydrates or fats (lipids)
• All carbohydrates are converted into glucose, which are then converted into energy.
• If you don’t use them all up, they will be stored as fat.
• Fats are converted to energy by being split into fatty acids and glycerol and then converted into energy (it takes a while).
• Our bodies will breakdown Fat (lipids) into energy IF we have used up all of our Carbohydrates. If you are starving your body will try and change the protein in your body into energy, but this is a last resort (you’re on your way to dying if this happens).

Our muscles hold 9 seconds of explosive energy at any time, therefore continuous replenishment is necessary.

Energy systems

The first myth I want to dispel is “your energy systems turn on sequentially”.  You use all energy systems continuously, which one depends on what you are doing.
The three energy systems we use are:

• Alactic (ATP/CP) – Anaerobic up to 9 seconds – think sprinter, weightlifter and shot putter.
• Lactic – Anaerobic – 9 seconds to 3 minutes hard training, depending on how much specific training you have done.  Think 200/400 metre sprints.  
• Aerobic – for those long easier distances and for doing day to day normal tasks.  Think anything that is not the above two.

For example:
100 metre sprinter = will mainly be in the Alactic and Lactic systems, this is where you get faster, stronger and more explosive.
A 10,000 metre runner = will mainly be in the aerobic systems, this is the system that with training will enable you to run a marathon and improve your cardiovascular health.
BUT both will use all energy systems.

Your body is the smartest machine known to man

Your body wants to get better, fitter and more efficient at everything it does. If you train it to do something, it will respond.  On the down side it will also respond to sitting and inactivity by decreasing your ability to move.  It makes you better at doing what you do a lot.

Adaptations to exercise

 When you start exercising  for example a run, this may feel anaerobic, your breathing will be heavy, your legs and arms will be heavy and a lot of Lactic acid will be released as it is new, this is important to remember  That doesn’t mean that it will always be that way, your body will very quickly adjust.

So, how much energy do we use?

So let’s have a look at the two training methods, Aerobic and Anaerobic.

Firstly it is important to point out that research has shown that your resting metabolic rate uses in percentage terms more energy (calories per day) than specific exercise, it works out at around 60% of your daily calorific allowance (even if you spend it in bed) That leaves 40% for movement.
It has been estimated that 3 x 30 min sessions of vigorous exercise per week increases energy demands by 1,039 Kcal/week. If average weekly calorific expenditure is 19,561 calories, then 1039 calories is only 5% of daily movement!

What is vigorous exercise? For ease let’s use the talk test, there are three levels to the talk test:

If you are exercising and able to talk in sentences – easy exercise (mainly aerobic)
If you are exercising and able to talk in short phrases – mainly threshold/lactic
If you are exercising and only able to utter one word at a time – mainly Alactic

In order to be doing the recommended 3 x 30 mins of vigorous exercise per week, you need to be in short phrase – one word category. Don’t underestimate how hard this training is.

Aerobic (cardiovascular)

Most people will lose a number of pounds and feel a lot fitter when they start aerobic training. This is because it is new to your body, (and in part because it is so new to your body, there is an element of the anaerobic to it) but as your body gets use to your training, adaptations occur that mean your body uses less calories to do the same exercise. This means that your body can transport and use oxygen more efficiently, it has created more capillaries and it has strengthened the bones and muscles being used. Once your body has adapted to this type of training, it is time to change it.


Firstly we have to be really honest about what constitutes an anaerobic workout If we go back to the beginning of this blog, in order to be anaerobically training we need to be engaging the Alactic and Lactic training systems or one word to a short phrase in talking. I see a lot of articles on High Intensity Interval Training (HIIT) which go on for 20, 30 and even 60 minutes as being anaerobic, it is not.   If you can do something for even 20 minutes continuously it is not anaerobic it is mainly aerobic.

Anaerobic training in running or cycling, the training intensity should be at 90 -100% and no longer than 2-3 minutes and should have a rest rate of equal or more in length, depending on the adaptations you are trying to achieve. This is tough training.

Once your body has adapted to the training even though it is at a higher intensity you would still need to change it again to keep getting positive adaptations. It does not matter how fit or experienced you are, if you change your training, adaptations will occur.


If you are a complete beginner then really you need an aerobic base with which to build onto an anaerobic training session. This can be just walking, swimming, jogging and light weights.  I wouldn’t advise doing it the other way round.

To the point

So if we go back to the original question about fat lose and exercise, to maximise fat loss we need to keep changing the intensity of our workouts, we need to keep making new positive adaptations.

But fat loss will not happen even with vigorous exercise, if your diet is not correct. What we put in our mouths determines how well we train, how well our body adapts and ultimately, how much body fat we carry, there is no cheat sheet….

So the answer is IT DEPENDS…. And it depends on you



Cardio Anaerobic
High-Intensity Interval Resistance Training (HIRT) influences resting energy expenditure and respiratory ratio in non-dieting individuals
Antonio Paoli, 1 Tatiana Moro,1 Giuseppe Marcolin,1 Marco Neri,2 Antonino Bianco,3 Antonio Palma,3 and Keith Grimaldi4

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