Energy – Working out – Fat loss
A quick tutorial on where it all comes from for Bodyfit.

By Stuart Salomon – Bodyfit Co-Owner

Our muscles have several different pathways they use to get energy to produce work. One way we lose weight is to work our muscles, which in turn takes energy(calories) to make them work. We are going to discuss how that energy is produced by the body and used by the muscles.

ATP is the source of energy for muscular contraction.

So, it is ATP that makes our muscles work. – Think of ATP as the energy molecule for muscles to contract. We have enough ATP in our muscles to work for about 4-6 seconds, after that we need to replenish that ATP.

First source of energy (or pathway) is CP

After the ATP pathway is exhausted, now we need to turn to the next pathway- which is the CP Pathway (Creatine Phosphate) – the CP is turned into ATP and we then gain about 15 seconds of muscular work out of this pathway before it is exhausted and we need to go to the next pathway.

Second Pathway of energy is Anaerobic Glycolysis

The Anaerobic pathway gets us about 40 seconds of energy for muscular contraction. This pathway is where we are breaking down Glucose in our blood to turn it into ATP to power our muscles. This is an extremely fast (but not as efficient as aerobic) conversion of glucose to ATP. This pathway does not use oxygen in it to convert the glucose to ATP. (hense the name anaerobic(without oxygen)). The byproduct of this conversion is lactic acid. We can only have so much lactic acid in our blood before we will be unable to use our muscles any more (burning sensation) and we need Oxygen to flush the lactic acid out. This is why we GASP for air when we do INTENSE exercise. We are sucking the oxygen in, to help flush that lactic acid out of our system. (oxygen is the critical ingredient to rid us of lactic acid) When we do Anaerobic exercise we create both oxygen debt, and lactic acid. This is when we do intense exercise (above our VO2 max).

***Note*** What is VO2? And what is VO2 Max?
VO2 Max is the maximum amount(volume) of oxygen that you can use during your maximum most strenuous exercise.

The third pathway of energy for muscles is Aerobic Respiration

This is when we replenish ATP from aerobic respiration. After about two minutes we have to switch from anaerobic glycolysis over to aerobic, and we have to start using oxygen to convert fuel to energy. In this case we are using Oxygen to create ATP, and it uses Glucose as the fuel – the byproducts are CO2 and Water- so the advantage is we do not make any toxic byproducts (lactic acid), and so therefore you can sustain aerobic exercise for a much longer period. In Aerobic Respiration- blood glucose is the primary fuel used, BUT your body can also use fat as an energy source (or protein in extreme cases, when no other fuel supply is available) You are always going to use the sugar (glucose) in your blood first to power aerobic respiration, but as the duration of exercise gets longer, and when it is of low intensity (50 to 60% of VO2 max) then your body will switch to fats as the energy source. This is why people talk about the “fat burning zone” where you do low intensity cardio for a long period of time. It is important to noted that the key component of Aerobic Respiration is that you must have oxygen for this process- and also this process can continue indefinitely.

OK…. So how do I take all this info and use it? How do I know what phase I am even in?
Forget science…Lets get to the good stuff!

Where do I want to train at? In an anaerobic zone? Or an aerobic zone?

This depends on how hard you want to work. HIIT is the rage these days, and HIIT operates in the ANAEROBIC PHASE OF ATP PRODUCTION. It is important to understand what HIIT is- this stands for high intensity interval training, and the key to this training is, we are taking our body to a state of exceeding our VO2 max for a short period of time (typically 30 seconds, usually one minute max) There is a difference between interval training and HIIT- in interval training we do not get to our VO2 max- in HIIT- we do. In this type of training we must rest after each interval- if the training is done right- then you MUST rest. The question is- Why do we need to rest? You must rest to clear your body of the lactic acid that is built up from the extreme training, this is caused by the anaerobic conversion of glucose to ATP to power your muscles. In HIIT training we only use about 35% of the energy from fat, and we use 65% of the energy from glucose in our blood.

So what about jogging on the treadmill or riding the bike, or any other activity that is considered traditional aerobic training? Is this good exercise? And what about that magic “fat loss zone” that everyone talks about. First off- any exercise is good exercise! The question is- how much is our time worth? If you have lots and lots of time- you can get results out of 60 minutes on the treadmill- absolutely. You will lose fat. Fat loss training is when we are at about 50% to 60% of our VO2 max. This is what we would call low intensity training and the key is that the primary energy pathway comes from stored fat in our body.

So why do HIIT? Why not just take a jog on the treadmill? It is a hell of a lot easier, that is for sure!

OK… so here is the trick- even though HIIT training does not use fat as the primary energy source, because your overall intensity of exercise is WAY WAY higher- you are overall using a lot more calories in the same given time. Even though you are using glucose as opposed to fat as your primary fuel- you are still burning more fat over the same period of time, because your overall calorie usage is so much higher because you are outputting so much more work. As a matter of fact, in doing HIIT training- you will burn the same amount of calories in one half to one third the time you would doing fat burning exercise where you stay at 50% of VO2 max. There is another important fact to note, in HIIT training you also supercharge your metabolism for about 19 hours after, after a 20 minute HIIT session- you will continue to burn calories for many hours after. At bodyfit we primarily focus on HIIT training.

Both traditional aerobic and HIIT as well as IT training are all going to have great health benefits, as a matter of fact the most recent research has revealed some interesting findings, ”IT ONLY TAKES 10 MINUTES A DAY OF MODERATE EXERCISE TO REAP MOST OF THE LONGEVITY AND DISEASE PREVENTION BENEFITS OF EXERCISE” Now that does not mean your going to have a great body, or lose weight- that just means even a small amount of exercise does wonders for you!

“There is no free lunch!”

Listen- you want to look good- u have to work hard. Do not think that a mild little work out is going to get you the body you want. That takes hard exhausting work- but for general health benefits, a little exercise goes a long way.


Here are some solid general guidelines.

1. Fat burning zone (aerobic respiration) – 50%60% of VO2 max – you can carry on a conversation with someone.
2. Moderate to right below high intensity (still aerobic respiration but right on the verge of the lactic threshold) – You can answer short yes or no questions- but cannot carry on a conversation
3. High intensity zone – above the lactic threshold. – (you are now producing lactic acid)- above 70% of VO2 max. – this is when you are gasping for air- your body needs the oxygen so badly to clear the lactic acid that you are not even able to utter a word till you get the O2 in you to clear the lactic acid from your mucles.


This depends on a few things- how good a condition you are in, how close you are really getting to HIIT vs IT training – are you REALLY getting to your VO2 max? a good start is double the amount of rest time to training time. 1 minute of intense training, 2 minutes of rest, a well conditioned athlete will actually do shorter cycles- such as 30 seconds on- 30 seconds off- and the 30 on/30 off cycle happens to correspond to the maximum calories that can can typically be used. Now here is a trick- when you are using short super intense cycles- exercise rotation becomes very important- this allows each muscle group to have more time to recover even though the overall amount of lactic acid in the body is increasing. Basically this rotation of exercise allows you to keep an overall higher intensity, closer to VO2 max, and more calorie burning.

Remember – intensity is key. So as an example – 30 seconds of clean and presses/30 rest/30 seconds of pull ups/30 rest/30 seconds of box jumps/30 rest - so the idea is that you are spreading the lactic acid buildup over your whole body, vs a single muscle group – and it allows for faster recovery of each muscle group while still keeping the intensity to your entire system up. For me- I am a big fan of 1 minute on, 1 minute off- because quite frankly that 30 on/30 off is hard! LOL – but remember- this is all about intensity- and all about how hard you push yourself to hit VO2 max and enter that anaerobic zone.
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