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If you’ve read any books on weightlifting, endurance sports, or training in general, you’ve probably come across the term energy system before.

Unfortunately, the more you read about energy systems, the more confused you’re likely to become.

Most explanations of energy systems quickly devolve into a complex firehose of scientific jargon like Krebs cycle, mitochondrial respiration, anaerobic glycolysis, and other tongue twisters.

Luckily, you don’t need a degree in exercise science to decipher energy systems. You don’t even need to know what most of these words mean.

At bottom, energy systems describe how your body produces energy during physical activity, from squatting a barbell to running a marathon to typing on a keyboard.

As you’ll learn in this podcast, gaining a better understanding of how energy systems work can help you improve your performance by optimizing your training and nutrition to support different energy systems, which in turn can improve your performance in different activities.

For example, have you ever wondered why your muscles begin to burn and you lose your breath when doing high reps?

Or why you start to feel tired after running for more than a few minutes?

Or why most people recommend you eat a lot of carbs to perform well as an athlete?

Energy systems hold the answers to all these questions.

What’s more, understanding energy systems gives you a much better idea of how to fuel your body for exercise, as what you eat can significantly impact the efficiency of different energy systems in your body.

In this podcast, you’ll learn:

  • How energy systems work
  • Why your body uses different energy systems during different kinds of exercise
  • How to eat and train to improve the efficiency of different energy systems
  • How improving one energy system in particular may help you gain muscle and strength
  • And more

Let’s begin.

Time Stamps:

3:53 – What is an energy system?

6:20 – What is the phosphocreatine system? 

10:54 – What is the aerobic system? 

18:22 – How do these energy systems relate to weightlifting? 

Mentioned on The Show: 

Books by Mike Matthews

What did you think of this episode? Have anything else to share? Let me know in the comments below!


Hi. Hey, hello, and welcome to another episode of Most For Life. I’m Mike Matthews. Thank you for joining me today to learn about energy systems, which sounds technical and it sounds academic and abstract. However, as you are going to learn in this podcast, it can be made simple and it can be made practical.

By understanding how some of your body’s primary energy systems work and how you can enhance them, you can boost your workout performance, which means, of course, better gains over time. Now, if you’ve tried to look into this before, you might have ended. Confused because you quickly ran into scientific jargon like the Crebs cycle and mitochondrial respiration and anaerobic like sis and other multi CIC tongue twisters.

Luckily, however, you do not need a degree in exercise science to understand. The grammar of this subject understand the fundamentals. You don’t even need to know what any of those words mean really, because at bottom energy systems simply describe how your body produces energy when you do physical things, whether it is squatting, a barbell, or running a marathon.

Just typing on a keyboard and as you will see or hear, rather, in this podcast, gaining a better understanding of how the energy systems, how the primary energy systems in the body work can help you better understand how to optimize your diet and your training in order to support and boost these systems, which again means better workouts and faster.

Progress. For example, have you ever wondered why your muscles begin to burn and you start to lose your breath when you are doing higher up training in the gym, or why you start to feel tired after running more than a few minutes? Or why most people recommend that you get a lot of. Carbs to perform well as an athlete.

The answers have to do with the bodies’ energy systems. Also, if you like what I’m doing here on the podcast and elsewhere, definitely check out my health and fitness books. Including the number one best selling weightlifting books for men and women in the world. Bigger, leaner, stronger, and thinner.

Leaner, stronger, as well as the leading flexible dieting cookbook, the Shredded Chef. Now, these books have sold well over 1 million copies and have helped thousands of people build their best body ever, and you can find them on all major online retailers like Audible, Amazon, iTunes, Cobo, and Google Play, as well as in.

Barnes and Noble Stores, and I should also mention that you can get any of the audio books 100% free when you sign up for an Audible account. And this is a great way to make those pockets of downtime like commuting, meal prepping, and cleaning more interesting, entertaining, and productive. And so if you want to take Audible up on this offer, and if you want to get one of my audio books for free, just go to Legion.

That’s b y And sign up for your account. So again, if you appreciate my work and if you wanna see more of it, and if you wanna learn time proven and evidence based strategies for losing fat, building muscle and getting healthy, and strategies that work for anyone and everyone, regardless of age or circumstances, please do consider picking up one of my best selling books, Bigger, Leaner, Stronger.

Thinner, Leaner, Stronger for women and the shredded chef for my favorite fitness friendly recipes. All right, so let’s start with a simple definition of what an energy system is. An energy system is a process your body uses to transform food you eat, and particularly the carbohydrate, protein, fat in the food you eat into a form of energy that your cells can actually use.

To do things to power, physical activity to stay alive. So what happens is you eat a meal and then your body breaks down the protein and the carbohydrate and the fat in the food into smaller molecules that it can use in different ways. So protein, for example, is broken down into immuno acids, which are primarily used as building blocks for the body of cells and tissues and amino acids are rarely used.

Energy to turn into something that the cells can use for energy. Whereas carbohydrate is broken down ultimately into a simple sugar called glucose, and that can be used either immediately for energy or it can be packaged into bundles to then be stored in the muscles and liver, and those bundles are called glycogen molecules.

And glycogen then can be easily broken back down into glucose. Energy is needed, especially during intense periods of activity like exercise, for example. Now fat is broken down into molecules called triglycerides, and then those can either be used immediately for energy or can be stored as body fat for future energy.

Needs because the body fat then can be broken down quickly into these simpler molecules, which then can ultimately be turned into very simple molecules that cells use for energy. Now what are those very simple molecules? They are called. Adenine tri phosphate ATP before any of the molecules I just discussed, the amino acids, the glycogen or glucose or the triglycerides before any of those can be used for energy by our cells.

They must be converted into this other compound, adenosine triphosphate, atp. Now the body has three energy systems it can use to supply its cells with atp, and which one or ones it primarily relies on? Depends on what’s going on. Depends on how quickly the body is burning through energy and how much energy it needs.

Now these three systems are the Phosphocreatine system. An aerobic system. And the aerobic system. So let’s start with talking about the phosphocreatine system. So of course we have to start with what is phosphocreatine? Phosphocreatine, which is also known as creatine phosphate, is a naturally occurring energy source found in muscle cells, and the body creates it by chemically modifying creatine, which is a molecule found in animal products, especially red meat and also creat.

Supplements and the phosphocreatine system is able to use this molecule, this phosphocreatine molecule, to generate atp, which then powers cells. And the main advantage of this system is that it can be used to generate a lot of atp. Very quickly. And that of course, makes it perfect for activities that require very brief and intense bursts of effort, like sprinting or very heavy weight lifting.

Let’s say a one rep max attempt or maybe a two or three rep set where you are ending very close to failure. Now, the downside of the phospho creatine system is that. The Phosphocreatine stores in the body are not very large. The body can only store a small amount of this stuff, specifically about enough to power 10 to 20 seconds of this very high intensity activity.

Now the body does naturally regenerate. Phosphocreatine, but it takes several minutes, like five minutes or longer for your muscles to be fully recharged, so to speak. Now, in case you are wondering how creatine supplements fit into this, how creatine impacts the Phosphocreatine system is, it improves the efficiency of this system.

It allows your body to create more ATP than it would be able to otherwise, and that’s how creating primarily how it improves performance. Now, you can also increase the efficiency of this system by doing a lot of this high intensity, brief, almost all out effort type of training interspersed with a lot of rest, But that’s only going to take you so far.

Now, if your body has enough Phosphocreatine to power through, let’s say 10 to 20 seconds of very high intensity effort, what happens after that? What happens is, Anaerobic system starts to take over. The anaerobic system starts producing the majority of the ATP for your muscles to keep doing whatever it is that you’re doing.

And this system is cold anaerobic because it regenerates ATP without the presence of oxygen and without aerobic oxygen. Now because this system does not need oxygen to produce atp, it can produce energy fairly quickly, but. Not as efficiently as the aerobic system, which we’ll talk about in a minute. The anaerobic system is also often referred to as the glycolytic system because it gets the majority of its energy from the glycogen that’s stored in the muscles and liver and the glucose in your blood.

So the main advantage of this anaerobic system is that it can produce a lot of. For about two minutes before it starts to peter out. And the main downside is that it produces a lot of metabolic byproducts that quickly build up in the blood and the muscles and these waste products cause fatigue and especially after the system has been running full bore for a couple of minutes.

Now the anaerobic system is particularly relevant to weightlifting because most of the work that you do in sets, and let’s say the range of eight to 12 reps are going to be powered by this anaerobic system. And this is also true for most forms of high intensity interval training where you alternate between bouts of sprinting and rest, and especially if the sprints are lasting longer than 20 seconds or.

Now as far as improving your body’s anaerobic system, the function of it, the best way to do that is simply to do a lot of anaerobic type exercise, which is not surprising. Of course. The more demands you place on that energy system, the more the body is going to augment it to meet those demands, and especially if you are continu.

Pushing the envelope through, let’s say, progressive overload in your training. So your training is progressively getting a bit harder on the body, and one of the ways it’s going to adapt is to strengthen the primary energy system that is powering that training. Okay, So we have intense physical activity going on for more than a couple of minutes.

What happens next? After a minute or two of continuous vigorous physical activity, the bodies. Aerobic system kicks in and takes over the function of producing a bunch of ATP for the muscles so we can keep on doing whatever it is that we’re doing, exercising, or again, just doing anything that is very physically demanding.

Now this system is also called the oxidative or the respiratory system. Because it uses oxygen, it involves oxygen to create the atp. Now it takes a few minutes for this system to really get into high gear, but once it is going, once it is firing on all cylinders, a big advantage is it can produce a lot of atp.

Very efficient. For a long time, and how it does that is it uses a combination of glucose, glycogen, and body fat to create ATP with the exact ratio, depending on how intense the exercise is. So as workout intensity rises, the aerobic system uses more and more glucose and glycogen to produce the ATP and less body fat, and is the workout intensity.

Falls, the aerobic system is gonna use more and more body fat and less glucose and glycogen. And this, by the way, is why many people believe that low intensity cardio is better or even best for fat loss and certainly more effective than high intensity cardio. Some people will say, because this low intensity cardio burns a greater percentage of calories from body fat.

Now, I spoke about this in my last q and a. I posted, I believe, So I won’t get into all the details again here, but what these people are missing is that higher intensity cardio burns a lot more total calories, which is really what drives long term fat loss. So while that high intensity interval workout did burn fewer calories from fat, In terms of a percentage than maybe a walk, it also burned a lot more total calories, which resulted in more total fat loss.

So this is simply a, an instance of missing the forest for the trees, right? Anyway, because the aerobic system can create a lot of ATP from body fat, that means that it can go for a long time, like hours on end because we all. A fair amount of body fat. Even the lean among us still have a fair amount of body fat that can be used for energy.

Body fat is very energy dense. It contains about three to 4,000 calories worth of energy per pound. And to put that in perspective, you’ll burn. Let’s say six to 700 calories per hour of moderately intense cycling and probably around 400 calories per hour of higher intensity weight lifting, the kind of stuff that you and I probably do.

And so if you look at those numbers, you quickly realize that we are carrying around a lot of energy in the form of body fat. So take me, I weigh 188 pounds right now. I am. 8% body fat. So I’m quite lean, which means I have about 15 pounds of fat on my body, which doesn’t sound like that much, but it represents about 53,000 calories, which is enough energy to get through about 70 hours of continuous biking or about double that in hours of intense weightlifting.

Now, of course, I would die before I would reach 0% body fat. You actually can’t get to 0%. Without dying, probably die around two to 3% as a man. But my point is just to give you an idea of how energy dense body fat is, and this is why, for example, you might have heard of case studies out. There of people with a lot of body fat who did not eat food for a very long time and they were given nutrients intravenously and they were given water but no food for a long time and there were no health problems and they just lost a bunch of weight and lost a bunch of fat in one case.

I remember reading about, there was a guy, I believe he started around 400 pounds and he worked with the doctor, so this was medically supervis. He didn’t eat food for an entire year. This was a year long fast. They gave him the basic nutrients, the essential vitamins and minerals, and the things that he needed to stay alive with water, of course, but no food for a year.

And in that year, he lost about. 200 pounds, he cut his body weight in half and he was much healthier than when he started. Because being extremely obese like that is extremely unhealthy. And that might sound wild, but when you think about how much. Energy is in, let’s say 170 pounds of fat because there’s gonna be some water and glycogen and other tissues that he’s going to have lost throughout that year.

Of course, not all gonna be body fat, but let’s say it was 150, 170 pounds of body fat. We know that my 15 pounds of fat would allow me to bike for about 70 hours straight before I will have run out of body fat. That guy had 10 times. The amount or maybe even a little more than that. And he wasn’t doing much in the way of exercise, of course, because he wouldn’t have had much energy and it wouldn’t have gone very well.

So it was mostly just basic movement that is required to stay alive and go about his day to day life, which of course does not burn that many calories anyway, to get back to the aerobic system. Something else that is worth noting. Some low carb advocates have misconstrued what we are talking about in this podcast and have come to the conclusion that since the aerobic system can use fat for energy, eating carbs isn’t going to improve your endurance performance or your performance on a run or bike or swim or so forth, and that is not.

True. It’s not that simple because while the aerobic system does allow you to exercise for hours at a time without eating any carbs, it only works if you keep your intensity around 60% of your maximum. If your exercise intensity exceeds about a six on a scale from one to 10, your body is going to need glucose to continue going.

And if your glycogen stores are low, then you are going to be severely limited in how much you’ll be able to do at that higher intensity level, and the only effective way to keep glycogen levels high in the body. Is to eat carbs. Now let’s bring all of this together in the context of weightlifting, which is probably what you care the most about, and that’s what I care the most about.

I do cardio because I do enjoy it to some degree, and of course it burns calories and it provides health benefits that weightlifting does not provide. And if you wanna learn more about that point, specifically checkout a podcast I posted probably about a month ago. On it called Should you do cardio?

If you lift weights, Science says yes, and you can learn all about that. You should be doing some cardio every week in addition to your weight lifting if you want to maximize your health and possibly your performance in your weight lifting as well. Which brings me to this last point I wanna make regarding how these different energy systems relate to your weight lifting.

If you like what I’m doing here on the podcast and elsewhere, definitely check out my health and fitness books, including the number one best selling weightlifting books for men and women in the world, Bigger, leaner, Stronger, and Thinni Leaner, Stronger, as well as the leading flexible dieting cookbook, the shredded.

As I mentioned earlier, when you are in the gym training, you’re probably training fairly intensely, and most of that is going to be powered by the Phosphocreatine system and the anaerobic system. But between your sets, when you’re resting and your. Catching your breath. Your body is going to be working to regenerate ATP before your next set, and it’s going to primarily rely on the aerobic system for that.

And so what you want then is you want of course, your phosphocreatine and your anaerobic systems to be able to work as efficiently as possible, but if you want to recover faster and to regenerate more ATP in the time that you are resting in between your sets, then you also want to have a strong aerobic.

Now as for strengthening your phosphocreatine and anaerobic systems, the best way to do that is to train in a variety of rep ranges, to periodize your training in a way where your muscles are regularly exposed to different rep ranges. So for example, in my program for. Intermediate and advanced weightlifters.

Beyond bigger, leaner, stronger. On the big compound exercises, you are working with weights ranging from about 95% of your one rep max to about 70% of your one rep max. And in terms of reps, at 95%, you may only do two to probably at most four reps, because when you are using 95% of your one rep max, you are actually doing an amrap.

So as many reps as possible, and you’re doing that at the end of a training block to see if you’ve gained strength in that training block. But as the weight is very heavy, you’re probably not gonna get more than four reps. Max five, you are certainly not gonna be getting eight, nine reps with what is truly 95% of what was your one rep max?

At the beginning of a macro cycle least? I’d say it’s very unlikely, as effective as. Program is, it is not going to be that effective for most people. And then in the case of 70% of one rep max, when you have 70% on the bar, the program is gonna have you do sets of 10. And with isolation exercises, the puration is similar, but the top of the rep ranges that you work in is a little bit higher.

So with isolation or what I call accessory exercises in the book, you are going to be doing sets of 10 to 12 reps. Those are gonna be your highest. Sets throughout a macro cycle and the weights will get heavier, and you will also be working in the rep range of six to eight reps later in a training cycle.

Now, there are several reasons why I think it makes sense to program like this when you are no longer a newbie. When you are now fighting for what’s probably your last 30% or so of muscle and strength that is genetically available to you, but as we are talking about energy systems in particular, one of the benefits of training like this is.

It provides plenty of stimulation for both the phosphocreatine and the anaerobic systems, and as those systems become more robust, the better your performance will be in the gym. I should note, however, though, that if you are new to proper weightlifting, so let’s say if you’re a guy who has yet to gain his first 20, maybe 25 pounds of muscle since beginning, no matter how long ago you started lifting weights, or if you’re a woman who has yet to gain maybe her first.

Eight pounds of muscle. You don’t have to program your training like that. You don’t have to periodize it the way that I’ve just described. You can train in a much simpler, more straightforward manner, and the books I would refer you to are bigger, leaner, stronger. If you’re a guy and thinni leaner, stronger.

If you are a gal, stick with those programs and you will gain all the muscle and strength that you can. Up until the point where those programs become more of a maintenance routine, and at that point it makes sense to switch to the beyond bigger, leaner, stronger program. If you’re a guy, and I do plan on creating a female version of that book, which will be of course beyond thin, leaner, stronger, but until that book is done and out, if you’re a woman, you can.

The men’s book and a lot of it will be directly applicable to what you’re doing. However, you will need some help minimally with updating the workout programming because it will probably have more upper body volume than you would like, and you would probably like to take some of the volume outta the upper body and put it into the lower body.

And I can help you do that if you just email. [email protected]. I will help you do just that. Okay? So that is really it as far as optimizing your phospho, creatine, and anaerobic systems. You just gotta work hard at it. Unfortunately, there are no biohacks or pills, powders, or potions that can do it for you.

As far as the aerobic system goes, just do some cardio, of course, and if you do, what you will probably find is within several weeks. Adding cardio to your routine. If you are not currently doing it, you will recover a bit faster in between your sets and you might even notice an increase in performance because what might happen is you are currently resting however long you’re resting in between sets.

You add cardio in your routine. You still only rest. Let’s say it’s two minutes in between the sets of isolation exercises, for example, and in those two minutes previously, your body was able to create. This much ATP now. However, because your aerobic system is more robust, it is able to create a bit more in that two minutes, which then manifests as better performance.

Now. As for how much cardio you should be doing, here’s a good place to start. Start with two or three. Low intensity cardio workouts, about 30 minutes a piece. Do something that is a low impact. Walking, cycling, swimming. And by low intensity, you should be able to carry on a conversation while you’re doing it.

Maybe you have to catch your breath here and there, but, If you are having to catch your breath fairly often, that’s now moderate intensity. So again, you should be able to carry on a conversation without really any effort at the low intensity band. Now, you can also do one or two high intensity interval cardio workouts per week if you really want to maximize the effectiveness of your aerobic energy system.

Now, if you’re gonna do that, I would say, Those sessions at no more than let’s say 25 to 30 minutes. And if you’re lean bulking, you can drop the high intensity out if you are afraid that it’s gonna cut into your progress in the gym. And there. Is an argument that can be made for that. Again, if you wanna get into these details more thoroughly, then check out that podcast that I recorded on why you should do cardio in addition to your weightlifting.

But just to keep it simple here, let’s say one or two hit cardio workouts per week, no more than 25 or 30 minutes per session, and I would say don’t do more than three and do. Low impact cardio. If you go and sprint on concrete, for example, you are going to beat up your lower body, and what you will almost certainly find is your squats and your deadlifts suffer.

I remember probably about eight years ago now, I was doing sprints, not on concrete, but at that time I was living on the beach and there was a boardwalk that would run along. The condo that I lived in, and I would run on that. So it wasn’t wood, it was probably, I don’t know, some sort of plastic that looked like wood.

However I just couldn’t recover from. It was only, I think I was doing two max, three sprint sessions per week, 15 to 20 minutes or so of sprints I would run about. I think maybe 80 to a hundred yards and then rest a couple of minutes, rinse and repeat. And what I found is, and so at that time I was like 28 and I was sleeping perfectly and eating perfectly.

I was as invincible as I could possibly be, and I still just couldn’t. Recover, especially my hip flexers. They were always sore and that would get in the way of my squatting and my quads and hamstrings. I could feel the soreness when I would start to squat or deadlift and it would take extra warmups just to feel up to any sort of intensity on those exercises.

And that was also when I was in a calorie surplus as well. So just keep that in mind with high intensity. Cardio is, if there’s any impact, it produces a lot of muscle damage that your body has to recover from. And if you’re also training intensely in the gym, it’s probably going to be too much. And even if it is not a high impact activity like cycling, which would be my personal.

Choice if I were to be doing hit cardio these days, but you can also row elliptical is good for that. Swimming is good for that. Still though that high intensity cardio puts a lot more recovery demands on the body than lower intensity cardio. And so if you’re cutting, for example, you just wanna maximize fat loss, you know you’re not gonna be gaining any muscle and strength, you’re just trying to preserve the muscle you have, and hopefully most of the strength you have, then it can make sense to add some hit into your routine because you’re gonna burn a lot of calories.

You are gonna burn fat faster, and so long as you don’t do too much, you don’t do too much cardio, you are not going to cause any degradation in your body composition. However, if you are lean, bulking, You might want to leave it out because you are really trying to just maximize your performance in your weight lifting.

And although adding the hit in will probably help you develop a slightly stronger aerobic system, there’s gonna be a trade off there. And if it’s me, I would leave the hit out. And I would just do low slash moderate intensity cardio to train my aerobic system. All right. That’s it for this episode. I hope you found it helpful.

And if you would like to let me know what you thought, shoot me an email, Mike and muscle, and share any and all feedback you might have about this episode or the podcast in general, or let me know if you have ideas for future episodes. And speaking of future episodes, here’s what I have coming.

Next for you. I have a C You episode coming in a couple of days where I’m gonna be talking about the mind muscle connection and slow rep training, as well as resting in between sets. How long should you be resting? Is three to four minutes too long? It definitely feels too long according to David e Barza, as well as my thoughts on why chasing money in success is not.

A waste of life. And then the following week I’ll be posting a new book club episode on a book called The Lost Tools of Learning and a new interview with the director of research and development of my sports nutrition company, Legion, about how we go about creating formulations and more. So if any of that got your attention, definitely keep an eye on the muscle for life.

All right. That’s it for this episode. I hope you enjoyed it and found it interesting and helpful. And if you did and you don’t mind doing me a favor, please do leave a quick review on iTunes or wherever you’re listening to me from in whichever app you’re listening to me in. Because that not only convinces people that they should check out the show, it also increases search.

Ability, and thus it helps more people find their way to me and learn how to get fitter, leaner, stronger, healthier, and happier as well. And of course, if you want to be notified when the next episode goes live, then simply subscribe to the podcast and you won’t miss out on any new stuff. And if you didn’t like something about the show, please do shoot me an email at mike muscle for, just muscle or, and share your thoughts on how I can do this better.

I read everything myself, and I’m always looking for constructive feedback, even if it is criticism. I’m open to it and of course you can email me if you have positive feedback as well, or if you have questions really relating to anything that you think I could help you with, definitely send me an email.

That is the best way to get ahold of me, Mike, at multiple And that’s it. Thanks again for listening to this episode, and I hope to hear from you soon.

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