The Engine Underneath: What Energy Systems Actually Are — Part 3 of 10
MY BJJ JOURNEY AFTER 40 • Post 3 of 10
By Juliano | Frames Culture
In the last post I told you about the realization that stopped me mid-podcast.
That the fatigue I was experiencing wasn't primarily an age problem. It was a training structure problem. That the way most of us train BJJ, hard rounds, moderate rest, repeat, puts the body into a metabolic zone that is exceptionally good at producing fatigue and exceptionally bad at producing recovery.
In this one, I want to explain what I mean by that. Because understanding it is the foundation for everything else that comes after.
And yes. This is the nerdy part I warned you about in Post 1.
The Tuesday Night It Clicked
I want to tell you exactly where I was when it all landed.
It was a Tuesday. I'd driven home from training, showered, and was sitting at the kitchen table with my phone, too wired to sleep and too tired to do anything useful. My wife had already gone to bed. I had a half-eaten bowl of rice in front of me and a YouTube video open on the screen.
I'd been doing this for a few weeks at that point. The research thing. Listening to Huberman and Attia on long drives. Searching things like why is BJJ so exhausting and recovery after 40 grappling and getting results that were either too generic or aimed at professional athletes with coaches managing their training load.
Neither of those was me.
But that Tuesday night, I stumbled onto something that explained, in about twenty minutes, why the last two years had felt the way they did. Not in a motivational way. In a mechanical way. The way understanding how an engine works explains why the car keeps stalling.
It was about energy systems.
How Your Body Actually Produces Energy
Your body has three ways of producing energy for physical work. They don't run in sequence. They're always operating at the same time. But depending on the intensity and duration of what you're doing, one dominates.
The Phosphocreatine System
This is your explosive system. It powers the first eight to ten seconds of maximal effort. The burst to shoot a takedown. The explosion to finish a submission attempt. The sudden movement to create a frame.
It burns clean, produces no significant fatigue byproducts, and recovers relatively quickly. Two to three minutes of rest and it's mostly recharged.
This system is not your problem.
The Glycolytic System
This is where things get interesting.
The glycolytic system takes over when the phosphocreatine system runs out, roughly from ten seconds of hard effort up to about two or three minutes. It's powerful. It can sustain real intensity. But it has a cost.
As it runs, the glycolytic system produces lactate as a byproduct. And more importantly, it produces hydrogen ions. Those hydrogen ions are what create the burning sensation in your forearms mid-round. The grip that suddenly won't close. The legs that stop cooperating. The breathing that gets ahead of you.
When people talk about hitting the wall in a hard roll, that is the chemistry of that moment.
(Here's the nerdy detail I find fascinating: lactate itself is not the villain. For years, people blamed lactic acid for the fatigue and the burn. The actual mechanism is the hydrogen ion accumulation, the drop in pH inside the muscle cell. Your body can actually use lactate as fuel. It's the acid environment that shuts things down.)
The Aerobic System
Slow. Clean. Efficient.
Powered by oxygen, fueled by a mix of glycogen and fat, and capable of sustaining effort for a very long time without producing significant fatigue byproducts.
But here's the part that matters most: the aerobic system is the primary mechanism for clearing the hydrogen ions produced by the glycolytic system.
It's not just an endurance engine. It's the recovery engine. The thing that determines how fast you bounce back between hard bursts. How quickly your grip comes back. How ready you are for round four after round three nearly broke you.
The goal isn't to train like you're 25 again. The goal is to build a way of training you can still be doing, and still enjoying, when you're 55.
The Problem No One Talks About in BJJ
Now look at what a typical BJJ round actually is.
Five minutes. Explosive bursts layered on top of sustained isometric tension. Grip fighting. Maintaining top pressure. Holding a tight guard from the bottom. Even the "passive" moments in a roll require sustained muscular effort that keeps the glycolytic system engaged.
A five-minute BJJ round is almost entirely glycolytic. Every scramble. Every desperate escape. Every surge to finish a sweep before the whistle.
And most gyms run short rest between rounds. Thirty seconds to two minutes, depending on the class format. That window is not long enough for the aerobic system to fully clear the hydrogen ions from the previous round. So you start round two a little more compromised than round one. Round three, more compromised still. By round four or five, you're running the glycolytic system on a platform that hasn't recovered, with fatigue byproducts already stacking from what came before.
Here's the part I didn't know after ten years of training:
Most BJJ practitioners have an underdeveloped aerobic system.
Not because they're unfit. Because rolling doesn't build it.
The aerobic system improves through sustained, moderate-intensity effort. The kind that feels almost too easy. The kind that looks nothing like a hard roll. If you've spent years doing nothing but five-minute rounds at high intensity, you may have solid glycolytic capacity and a mediocre aerobic base underneath it. Which means you can go hard. You just can't recover from going hard very quickly.
Peter Attia writes about this in Outlive. He describes the aerobic base as the foundation layer of physical capacity, the thing everything else sits on top of. Neglect it, and the layers above become unstable. Most people, he argues, spend almost all their training time in the middle of the pyramid and almost none of it at the base.
In BJJ, we don't even think about the base. We just roll.
What This Looked Like in My Own Training
I opened a notes app that Tuesday night and tried to map out a typical training session.
Five-minute rounds. Sixty seconds on the wall between them. Maybe some drilling beforehand, which is also glycolytic. Repeat for ninety minutes.
Every round: glycolytic.
Every recovery window: too short for the aerobic system to do its job properly.
I'd been training this way, the way almost everyone trains, for a decade.
And for the first several years, it didn't matter much. I recovered fast enough that the structural inefficiency was absorbed. My body had the hormonal resources, the mitochondrial capacity, the nervous system resilience to absorb the load and bounce back.
Then I turned forty. Then forty-two. Then forty-five.
The recovery cost didn't stay the same. It went up. Gradually, then noticeably. And I kept training the same way, wondering why the results felt different.
The Moment of Relief
I sat with all of this for a while.
Then I felt something I hadn't felt in about two years: relief.
Not because the problem was solved. Because the problem had a name. And problems with names have solutions.
I wasn't broken. I wasn't declining faster than I should be. I was running a high-demand glycolytic sport on an underdeveloped aerobic engine, with less hormonal recovery support than I'd had at thirty, doing it the same way I always had, without ever asking whether the approach needed to change.
That's an engineering problem. And engineers fix things.
There's a concept I keep returning to from Post 2: fatigue is information, not a verdict. Understanding energy systems is where that idea stopped being abstract and started having actual content.
The fatigue after a hard session isn't telling you that you're too old for this. It's telling you that your glycolytic system is doing more work than your aerobic base can efficiently recover from. Those are different problems with different solutions.
What Comes Next
The obvious question, once you understand how the energy systems interact, is this: if BJJ training is almost entirely glycolytic, and the aerobic system is what enables recovery from that work, why doesn't BJJ training build the aerobic system?
The answer matters. A lot.
And it connects directly to why the way most of us train after 40 is almost perfectly designed to keep us stuck.
That's what I want to get into next week.
Resources Referenced in This Post
Book: Outlive: The Science and Art of Longevity — Peter Attia, MD
Book: Why We Sleep: Unlocking the Power of Sleep and Dreams — Matthew Walker, PhD
Podcast: The Peter Attia Drive — episodes on Zone 2 and aerobic base
Podcast: Huberman Lab — Andy Galpin guest series on fitness and recovery
When do you notice fatigue most during a training session? Is it the first round, or does it build across rounds and hit you later? How does round four feel compared to round one?
Send me a message. I read every response, and your answers directly shape where this series goes.
And if you're going to keep showing up to class, you might as well look good doing it.
 Masters: Still Here BJJ T-shirt |
 Old Man BJJ T-shirt |
 Crunchy BJJ T-shirt |
 Embrace Discomfort BJJ T-shirt |
Next week:
In Post 4, I get into exactly why BJJ is structured like an energy trap, and why that trap gets harder to escape the older you get. Once you see it, you can't unsee it. See you then.