You’re Not Unfit — You’re Metabolically Inflexible
How Zone 2 Cardio Rebuilds Your Energy Systems, One Heartbeat at a Time
You’re Not Hitting Your Goals
Because You’re Skipping the Work That Actually Works
Not because you’re lazy.
Because no one told you the truth about low-intensity training.
Fitness isn’t about going harder or chasing sweat angels.
More HIIT ≠ better results.
It’s like punching yourself in the face and expecting to get stronger.
You’ll feel tired. But you won’t adapt.
What actually builds endurance, fat-burning capacity, and metabolic health?
Zone 2 training.
Old-school endurance athletes have done this forever — long slow distance (LSD), aerobic base work.
There’s a lot of hype around Zone 2. While it isn’t (nothing is) a magic pill, if your gap is Zone 2 training, then it will make a dramatic difference.
Zone 2 improves mitochondrial function, metabolic flexibility, and longevity. (Cited in journals like Cell, PubMed, and more).
The problem with Zone 2 training?
Most people skip it. Or do it wrong.
Let’s fix that.
This article (and Zone 2) is for you if:
your resting heart rate is 60 or more.
your body fat percentage is high (>20% for men, >30% for women).
your stamina is poor.
you don’t lose body fat, despite regular exercise
What Is Zone 2 Cardio?
Zone 2 is a heart rate zone where your body:
Primarily uses fat for fuel
Produces minimal lactate and metabolic waste
Maximises stroke volume of the heart
Keeps mitochondria working efficiently
This is aerobic base training.
Clean energy, low fatigue, high adaptation.
At this heart rate, two major things happen:
Stroke volume peaks — your heart pushes out more oxygenated blood per beat
Mitochondria hum — the power plants of your cells work at their most efficient state
Polar (yes, the HR monitor company) defines Zone 2 as 60–70% of max HR. But it’s better to use individualised tools like the MAF formula:
180 – your age = target heart rate (±5 bpm buffer)
Before we dig into application — let’s revisit how your body produces energy.
Energy Systems: The Physiology Behind Fatigue
You have 3 systems for energy:
1. Alactic (ATP-CP System)
Sprint 50m. Pure power.
No oxygen needed. No waste.
Runs out in ~10 seconds.
2. Glycolytic
400–800m run, HIIT, CrossFit.
Fast energy from glucose.
Produces hydrogen ions (H⁺) → causes acidity and fatigue.
3. Aerobic
Long runs, Zone 2, LSD.
Fat is the primary fuel.
Low waste, high sustainability.
Zone 2 = maximum aerobic development without shifting into glycolysis.
I learned this the hard way.
My Own Wake-Up Call
At the 2015 World Championships of Beach Ultimate, I was strong and fast.
I could swing heavy kettlebells, sprint hard, and cut sharply.
But during long points?
My breathing fell apart
My mind lost focus
I couldn’t repeat sprint efforts
I had a poor aerobic engine.
Strength without endurance is like a Ferrari with no fuel tank.
Most People Aren’t In Zone 2 — Even When They Think They Are
Case in point: I once did a 5K at what I thought was an “easy” pace - 30 minutes instead of my usual 25.
Surely Zone 2 or 3?
Nope.
Zone 4 and 5 the entire time.
That’s the trap. Your ego says “easy.”
Your heart rate says “lol, no.”
Lactate Isn’t the Problem — Acidity Is
The burn? The soreness? The “feel the pain” mentality?
It’s not lactate doing that.
Here’s how it really works:
Glycolysis → ATP + H⁺ ions
Intense effort = fast glucose breakdown → acidity rises → fatigue kicks in
Lactate = the buffer
It’s made to mop up excess H⁺ and transport it out of cells via MCT transporters
Lactate is recycled as fuel when oxygen is available.
“Lactate is not a dead-end waste product… but a key intermediary.”
George Brooks, Lactate Shuttle Theory
Once I stopped chasing the burn and focused on minimising waste, my recovery improved. My energy returned.
And my performance shot up.
Mitochondria: Your Real Metabolic Engine
Zone 2 triggers two major mitochondrial upgrades:
Biogenesis — more mitochondria per cell
Mitophagy — removal of dysfunctional mitochondria
This makes your body better at:
Burning fat
Resisting fatigue
Recovering faster
Improving insulin sensitivity
Sustaining high output over time
It’s not just theory. Zone 2 is being studied for:
Zone 2 is how you train your cells — not just your body.
The Metabolic Flexibility Shift
Most people are “stuck” in glucose-burning mode — even at rest.
That’s metabolic inflexibility. It leads to:
Constant cravings
Energy crashes
Insulin resistance
Difficulty losing fat
Overtraining without results
Metabolic flexibility = your ability to switch between fat and carb usage depending on intensity and availability.
Think of it like a hybrid car.
Zone 2 is what teaches your body how to run on electricity (fat) — not just gasoline (carbs).
My Own Transformation
During intense strength phases, I gained fat - despite lifting 5–6x/week.
Going harder didn’t work.
So I dialled back intensity, kept lifting light, and prioritised Zone 2.
In 8 weeks, I lost 6 cm off my waist.
Strength intact. Energy better. Recovery faster.
Identify your strengths and gaps
Once again, let me reiterate Zone 2 is not the magic. It was a huge gap in my physical ability matrix. Using The Quad method, I plotted my strength, endurance, mobility, and power. And I could see that one specific aspect of my endurance (Zone 2) was far behind the rest of my physical attributes.
Using this framework, I’ve been able to plot the shortest path for me and my students.
How to Build Your Zone 2 Engine
Step 1: Find Your HR Zone
180 – your age = top end of Zone 2
Buffer ±5 bpm based on fitness, recovery, or illness.
Step 2: Follow This Progression
Step 1: For the first 2 weeks
Start with 3 sessions of 30 minutes per week.
Keep your heart rate between 120-140 bpm (as per the example.)
Remember, you need to calculate your band.
Your band is 180-age to 160-age.
Step 2: For weeks 3 and 4
(or) after you’ve gotten 2 weeks of 3 sessions each
Increase to 4 sessions of 30 minutes.
Keep the heart rate in the same band.
Step 3: Once you are stable at 4 sessions, do this for 2 weeks.
Increase two of the sessions to 45 minutes.
Keep two of the sessions at 30 minutes.
So, you are doing 2 x 30 minutes and 2 x 45 minutes every week in Zone 2.
Step 4: Once you stabilise 150 minutes per week in Zone 2 …
Increase it to 180 minutes per week.
You can do that in one of the two ways below:
4 x 45 minutes
2 x 30 minutes and 2 x 60 minutes
When you get 2 weeks of 180 minutes per week, go to step 5.
Step 5: 210 minutes per week
Increase weekly duration to 210 minutes.
You can add a 5th session to the week, if you can.
Do this for 8 weeks.
At the end of that, you will have:
lost a lot of body fat.
improved your metabolic flexibility.
have a lot more energy during the day.
and ready to kick on to bigger things in your fitness and life.
A few things to keep in mind:
Start slowly, even though it is low intensity.
Breathe through your nose
More sessions are better than less sessions.
That is, do not do a 2-hour session and a 1-hour session each week.
4 x 45 minute sessions is better.Keep the sessions between 30-75 minutes long.
Stay in the heart rate zone.
What activity to do:
Any cardio activity works as long as the heart rate rule is obeyed.
Brisk walking or jogging
Cycling
Swimming
Rowing
Indian clubs / Light steel clubs
Erg and ski-erg
You can also combine the above i.e. do 15 minutes of one, then 15 minutes of another, and finish with 15 minutes of a third.
Why Zone 2 Works (Even if You Lift)
Zone 2 improves:
Heart Rate Variability
Fatigue resistance
Metabolic flexibility
Nervous system resilience
Mitochondrial health
Inflammation reduction
You’ll feel better. Recover faster. Lift more. Sleep deeper.
Closing Thoughts: Build the Engine First
Fat loss. Focus. Energy. Recovery.
It all comes back to your aerobic base.
Too many people train too hard, too often.
They think they need more motivation — when they actually need Zone 2.
If you’re metabolically inflexible, overtrained, or just tired of hitting walls — start here.
Slow down. Stay consistent.
And watch your entire fitness ecosystem level up.
If you’d like to learn more about this topic, here are a few things for you to dive into.
Mitochondria
Read More
Systematic Review: Exercise Improves Mitochondrial Function in CVD Patients
Aerobic exercise significantly enhances mitochondrial oxidative capacity and biogenesis—especially at lower intensities. Succinate-involved oxidative phosphorylation improved most with moderate aerobic training.
Exercise training significantly improved mitochondrial oxidative capacity and antioxidant activity... especially through aerobic modalities.
ABC Science Feature on Zone 2 Training
Zone 2 boosts mitochondrial quantity and function, improving fat oxidation and extending endurance.
Zone 2 increases both the number and efficiency of mitochondria. It enhances the body's ability to metabolise fat and sustain output.
Comparative Study: LSD vs. HIIT and SIT
This study compared mitochondrial adaptations across three training modalities. They were Long Slow Distance (LSD), Sprint Interval Training (SIT), and High-Intensity Interval Training (HIIT).
LSD showed effective mitochondrial improvements, especially for endurance development.
Endurance training at lower intensities is great at promoting mitochondrial adaptations.
INSCYD Breakdown: Zone 2 & Mitochondrial Function
Zone 2 increases your ability to generate aerobic energy from fat and lactate. It boosts both fat-burning and lactate-clearing capacity.
Zone 2 training increases the number and function of mitochondria. Which translates into improving your metabolic engine’s efficiency.
Metabolic Flexibility
Metabolic Flexibility in Health and Disease
Explores how fuel switching is regulated and impaired in conditions like obesity and insulin resistance.
Metabolic Flexibility as an Adaptation to Energy Resources and Requirements
The liver, adipose tissue, and muscle govern systemic metabolic flexibility and manage nutrient sensing, uptake, transport, storage, and expenditure by communication via endocrine cues.
At a molecular level, metabolic flexibility relies on the configuration of metabolic pathways, which are regulated by key metabolic enzymes and transcription factors, many of which interact closely with the mitochondria.
Disrupted metabolic flexibility, or metabolic inflexibility, however, is associated with many pathological conditions including metabolic syndrome, type 2 diabetes mellitus, and cancer.
[…] patients with metabolic syndrome (MtS) are characterized by a decreased capacity to oxidize lipids and by early transition from fat to carbohydrate oxidation (FATox/CHOox), as well as elevated blood lactate concentration [La-] as exercise power output (PO) increases, a condition termed 'metabolic inflexibility'.