A New Look under the Hood


This is post taken from Barry’s Patreon account. The Connected Athlete. This is a new portal where Barry writes about all the facets connecting athletes with health and performance. He also records a podcast with professional cyclist Svein Tuft which goes into the detail and practice of the various topics. For those who are interested, you can sign up here: 

All those scribbles in the image above are the various metabolic pathways in your cell.

We are complex machines. Yet, today we seem to want to reduce things and put brackets around everything. Don’t get me wrong, I think the ultimate goal is to simplify the complexity. However, it needs to be done in the Einstein way, by making things simple but not simpler. Saying that we burn just carbs at a certain intensity and fats at another, is making things simple but also simpler. There is a lot more to it as we are far more sophisticated than that.

This , in my opinion, is how we are getting things wrong regarding nutrition and fueling. As I have stated from the outset, everything is connected. In terms of energy production, the pathways in our cells are all connected too.
That’s why it kills me when I hear the standard approach and debate regarding energy that we need “carbs” to go fast and can only use “fats” to go slow and steady.


This is a classic reductionist view and it alludes to us having a binary energy system. Just look at the image again , does it look like we just have two energy pathways ??


Of course it doesn’t, which is why it is complete nonsense to have the idea that:


Carbs (that you have to eat)  ——–> ATP (quick energy)


Fats —————————> ATP (slow energy)


Which is generally the understanding for most people that debate and argue this point. Even the academics, not all of course, do the same.


I’ve been looking at metabolic pathways, the big picture above, since I was in college doing biochemistry. that was 20yrs ago. And it still melts my head and I still don’t understand it all. Plus, as I will explain later, we haven’t even fully worked out how our cells function. Remember, it was only 50-60yrs ago that we mapped out the mitochondria but we started evolving on this planet 7-8million years ago. So you could say, we are still getting to know ourselves.


Anyway, what I want to do is give people an overview, that is somewhat easy to follow, of how we do and can make energy. By understanding more you are able to do more. Simply thinking you have a carb engine and a fat engine means you are not aware of the other systems. If you are not aware then you are not as likely to know how to use them or optimize them.


Its sort of like having a a nice big V12 engine but only using 2 of the pistons to drive the crankshaft. The car will still go, but not very fast or smooth. Get the other 10 pistons going, the V12 starts working the way it is designed to work, and the car goes fast and smooth.


In the case of our engine , the mitochondria, the pistons are not all the same size and some of them are hard to find. However, just like the V12, the mitochondria works best when all the pistons are firing.


Back to how this makes you a more connected athlete. So if you know that you have several other systems to activate, you will look into the ways in which to do so. In order for the adaptation to occur, the stimulus must resonate.


If those stimuli can come from your nutrition, your training , your lifestyle and your environment, then you start realizing that you’ve been trapped in comfort for too long. The comfort is the bracketed research/guidelines/recommendations that you think is all you have to follow. But when you start learning about how the human body truly functions and what we still don’t know, then you start to look outside the box.


This is the essence of becoming connected. We live in a one dimensional world of sports nutrition and sports physiology. We’re told specific percentages and figures, like we can only burn a maximum of 1.1g/min of fats , that if we go over 70% effort , we can only burn carbs, that we need 60-90g carbs/hr during races and that we can’t sweat more than 2% of our body weight, that we need to train at certain heart rate zones and specific intensities. That we burn x amount of calories per hour. The list goes on and on. 


What I’m saying is that when you put the 3D glasses on, you see how all these laws and rules can be broken. Not just blatantly broken, but that we have the physiological capability to break them in terms of our cellular design. Then you see them happening in real life, and what really convinces you, is when it starts happening to yourself. I’ve set pb’s for short distance runnning races, 5 and 10k, on very low carb intake. I’ve won ultramarathons, that have lasted several hours, without consuming anything close to 60-90g/hr. When Haile Gebrselassie broke the world record for the marathon in 2008, he was reported to have lost 10% of his body weight.


We are capable of more than we are told. Once you have the understanding, you will have the belief. Once you have the belief, you are able to put the words into action. I see this all the time with the athletes I work with and it has been my own personal experience too. 


So lets look at how we can harness energy in terms of the source and the pathways:


I will say I got a bit of a writers block when I started writing this. I thought I knew it all, but I didn’t really fully comprehend it all. When you are in this game, it is sometimes easy to think you know stuff. Then when you really look into it, you realize you have to study a lot more. So I have decided to summarize and sort of gloss over everything as every sub heading below needs its own separate post. But for now, its an overview that most people will have never seen before:


First up, lets outline how and where we can source energy from:


Adipose Tissue Fats – Lipolysis


This is the breakdown of triglycerides stored in adipose tissue into glycerol and fatty acids. These are released then into the bloodstream and transported to the mitochondria to be used as fuel. A typical 70Kg male athlete with 10% body fat, has 7kg of fat stored in adipose tissue. That would be a fairly light lean individual . Still, they have 5-6% body fat that can be burned as fuel… still leaving them with the minimum requirement of 4-5% to stay healthy.


5-6% body fat = 3.5-4Kg = ~35-40,000kcal
That’s still a lot of energy. Burning ~600kcal/hr… that lean fit athlete can go for a long time on his own fat. Becoming fat adapted enables you to better access it. But even at low/non HIT type exercise… if you burn 600kcal/hr… and you can use your own body fat as the fuel… thats a lot of hours worth of energy.


Intramuscular Triglyerirdes 


IMTG’s or Intramuscular fat is fat that is stored in skeletal muscle. It is stored close to mitochondria and athletes have be shown to be able to store increased content.


This makes IMTG’s much more usuable as an energy source compared to adipose tissue since it does not have to travel far. Endurance athletes have been shown to store more and use more during exericse.


Not a huge amount of studies done on this. Reports show IMTG storage in the muscle in the range of 2-4,000kcal. Diet and training, increase the storage i.e. higher fat diets and fasted training. So it could be even more. Given that a marathon, 3hrs, decent pace, 800kcal/hr…. means that if you are using your IMTG’s for fuel, you could run the marathon fuels on your muscle fats.




A polymer chain of glucose molecules stored in the muscle and liver. A 70kg individual can store ~100g in the liver and ~400g in the muscle. Glycolysis breaks glycogen down into glucose which can then be coverted into energy both anerbolically and aerobically.


500g of glycogen = 2,000kcal.
Therefore, the 3hr marathon runner above, requiring 2,400kcal, cannot run solely on carbohydrates stored. For cyclists, Ironman, ultrarunners.. that race for several hours, can definitely not rely on glycogen as their only energy source.




Glucose production in the liver from non carbohydrate sources such as glycerol and amino acids. This means, you can make your own glucose which can get converted to glycogen and stored in the liver. Crucial point to be aware of. 


Let me rephrase this. You have others ways to make glucose without consuming it. The 3 major sources are Glycerol , Glycolytic Amino Acids and Lactate. In terms of experience/trained athletes, we don’t know exactly how much. However, there is reasoning (and I think studies) to show that we can become better adapted to using gluconeogensis. Like everything, if the stimulus is there, the body can adapt.




Conversion of lactate back to glucose in the liver which can be resupplied to the muscle. This happens during anaerboic exercise. So you burn glucose, it gets converted to Pyruvate, and if there is not oxygen there, it gets converted to Lactate. This lactate goes back to the liver, gets converted  back to Glucose, and this can then be delivered back to the muscle. And again, the more trained and the more adapted you become, the better able you can do this.




The breakdown of fatty acids to Acetly-CoEnzymeA . This is the precursor for the Krebs/TCA cycle in the mitochondria.


Lets makes this very clear. Aerobic Glycolysis, which is our main energy production pathway for exercise, starts with a precursor. Glucose has to get converted to this precursor in order for the Krebs cycle to begin.


Fats, can get converted to the exact same precursor, Acetly-Coenzme A, and enters the exact same Krebs Cycle. 




The production of ketone bodies, which can also be supplied to the mitochondria.


Once again, these ketones can be converted to the precursor for the Krebs Cycle. But as mentioned and discussed in previous posts, ketosis requires mainly VLC and fasting plus we are unsure as to how ketones are used in the muscle during intense exercise. Key point to note, is that its potentially another energy source.


Okay, on to Energy Systems:


Phospho- Creatine System


Creatine Phosphate, stored in the muscle, can provide a Phosphate that bonds to ADP to give ATP. This happens without the need for oxygen or the production of lactic acid. It is the energy provided for up to 10seconds of explosive work e.g. sprinting, lifting. 


PCR + ADP —–>    ATP + Cr
Anaerobic Glycolysis 


This is the breakdown of Glucose to Pyruvate and ATP. There is no need for oxygen in this pathway. Energy can be generated for 1-2mins of high intensity exercise. The Pyruvate is converted to Lactate in the absence of oxygen. 


Glucose —->    Pryruvate + ATP


Aerobic Glycolysis or Oxidative Phosphorlyation


This is when Pyruvate enters the mitochondria and is converted to Acetly-CoenzymeA . This is the molecule that starts the cycle of a series of chemical reactions that uses oxygen to produce ATP and carbon dioxide.


This cycle is known as the Krebs Cycle, Citric Acid Cycle or Tricarboxylic Acid Cycle.


During this cycle, NADH is formed which can donate electrons. The release of electrons from a donar to an acceptor is know as a redox reaction. These redox reactions release energy which can be used to form ATP and are carried out by protein complexes. 


The energy released by electrons flowing through this electron transport chain is used to transport protons across the inner mitochondrial membrane, in a process called the  electron transport chain (ETC). This generates potential energy in the form of a Ph gradient and an electrical potential across this membrane. This store of energy is tapped when protons flow back across the membrane and down the potential energy gradient, through a large enzyme called ATPase; this process is known as Chemiosmosis. 


The ATP synthase uses the energy to transform Adenosine Diphosphate (ADP) into adenosine triphosphate, in a phosphorylation reaction. The reaction is driven by the proton flow, which forces the rotation of a part of the enzyme; the ATP synthase is a rotary mechanical motor.


Just look at this picture of the ATPase molecule. Its the most sophisticated and impressive nanomachine  we have to produce energy. And it doesn’t run on carbs or fats.


The ATP generated from the Krebs Cycle can be used for prolonged exercise. The more trained you become, the faster you can go for longer, using this energy pathway.


Pentose Phosphate Pathway


The pentose phosphate pathway is an alternative to glycolysis and generates NADPH (oxidative phase) and pentoses (5-carbon sugars, nonoxidative phase). It also metabolizes dietary pentoses (e.g. Ribose) and provides glycolytic/gluconeogenic intermediates. NADPH is required in anabolic reactions, such as fatty acid and nucleic acid synthesis and the reduction of glutathione. Remember also that NADPH is the proton donor that is used by the protein complexes of the Electron Transport Chain. It is NADPH that gives H+, and this proton flow helps drive the rotary engine of ATPase converting ADP to ATP.  The PPP can generate large amounts of NADPH which can also be used to reduce oxidative stress and hence lower inflammation. Pentoses, in particular ribose-5-phosphate, are utilized in the synthesis of nucleotides and nucleic acids.


Very little is known about this pathway in terms of its role in exercise and in the muscle cell. For now, I just want to highlight that this pathway exists and that it does produce glycolytic intermediates for glycolysis and it does reduce oxidative damage.


If you do want to delve further, let me redirect you to one guy who is much further down the tunnel. This is very advanced science and is certainly not for beginners. However, if you want to read something that is closer to the truth than the standard current model, then this is as close as it gets:



Quantum Systems


This is head melting stuff and is really only a very recent branch of science now known as Quantum Biology. 
Lets keep it simple for now. Quantum means small, very small, subatomic particles.


Protons and electrons are subatomic. The motor we have in our mitochondria to produce energy (ATP) is driven by the flow of protons and electrons. Not carbs or fats. This is a simple but crucial point. 


ATP is our universal energy current. Each cell can use 10million molecules of ATP every second. There are about 40 trillion cells in the human body. That means the total ATP turnover is 60-100Kg per day. So this energy, that we produce in massive quantities, our own body weight on a daily basis, is made from electrons and protons. (I pulled this from the book called –The Vital Question by Nick Lane).


So we essentially have quantum energy production. This means, what affects this process needs to be assessed using quantum theory.


What does this mean to us ?


All I can say for now is that this means the way in which we produce energy is not totally understood. It means there may be other mechanisms that affect energy production. It could mean that we can produce energy outside of the calorie model. This might seem plausible for those of us who have experienced “impossible” situations in our athletic endeavours. There have been many occasions where the maths just don’t add up. 


So maybe, perhaps, we have far more sophisticated mechanisms for producing energy that we haven’t quite figured out yet.


“If there is something in nature you don’t understand, the chances are it works in far more sophisticated ways than you thought”


The next time someone tells you that you need to eat a certain amount of carbs to fuel…. send them this blog.

Leave a Reply