Aerobic Threshold: The Fitness Metric You’re Probably Ignoring
- Ronan
- May 7
- 6 min read
Fed up with hitting the wall during workouts?
Stubborn fat refusing to budge despite endless miles? You might be missing the most crucial piece of your fitness puzzle - knowing your aerobic threshold.
We're obsessed with numbers, aren't we?
And one of the most sought-after is VO2max - that impressive-sounding number that supposedly defines our fitness potential.
It is incredibly important, that much is true...
...but what if I told you there's another metric that could transform your training, rev up fat burning, and maximise your endurance — and it's one that most people completely ignore?
Meet Your Aerobic Threshold: Your Body's 'All-Day' Gear
Let’s get straight to it. Your Aerobic Threshold is the specific exercise intensity at which your body is still able to primarily use fat for fuel, while clearing lactate (that stuff often blamed for muscle burn) as quickly as it's produced.
Imagine this: Your body has two fuel tanks:
A massive one filled with fat (even the leanest people have enough stored fat calories to run multiple marathons)
A much smaller one, full of carbohydrates (stored as glycogen)
At very low intensities (like a gentle walk), you're cruising, mostly sipping from that big fat tank. ;)
Easy peasy. However...
As you ramp up the intensity, you start to draw a bit more from the carb tank.
Your Aerobic Threshold (AeT) sits at that crossroads. This is your 'cruising speed' where you’re still using mostly fat for fuel, producing very little lactate, and feeling pretty comfortable – like you could go for hours. It's often referred to as your Ventilatory Threshold 1 (VT1) or First Lactate Threshold (LT1) in lab tests, where breathing is increased but comfortable.
Push much beyond that, and you’ll cross another point – your Anaerobic Threshold (AT, or VT2) – where your body relies much more heavily on carbs, lactate starts to build up, and the "this is hard" feeling kicks in.
But...! Training around your AeT isn't just about "going easy" and see how it feels.
It’s a precise physiological marker, unique to you.
Knowing it means you can train smarter, not just harder, to specifically develop your aerobic base – the foundation of all your fitness.
Why Your Aerobic Threshold is a MUCH Bigger Deal Than You Realise
Ignoring your Aerobic Threshold is like owning a fancy car but only ever driving it in first or fifth gear – you’re missing out on the smoothest, most efficient ride.
Here’s why:
1. It Builds Monster Endurance
Training at or just below your AeT creates powerful adaptations:
More mitochondria (your cellular powerhouses)
Increased capillarisation (more blood vessels feeding your muscles)
Enhanced oxygen utilisation
The result? You can go longer, recover faster, and feel stronger - whether you're running a 10K or just keeping up with your kids.
2. It Turns You Into a Fat-Burning Machine
When you train around your AeT, your body becomes really efficient at using fat for fuel:
You begin to burn more fat at higher exercise intensities: Instead of quickly switching to carbs, your body learns to use fat for longer as you exercise.
Spares precious glycogen: By burning more fat for fuel, you save your limited carbohydrate stores for when you really need them (like that final sprint or hill climb).
Improve body composition: Consistent AeT training helps chip away at body fat because you’re teaching your body to tap into those reserves more readily
Don't pay too much attention to "fat-burning zones" on your smartwatch - the readings aren't' always super-accurate and are based on algorithms. Your AeT defines YOUR optimal fat-burning intensity, and it can be measured.
Note that AeT while is not exactly the same as another often used term 'fat max' (the exercise intensity at which fat burning is maximised) they are often very close together.
3. It Makes Training Sustainable (and Enjoyable!)
Let's be honest — constantly flogging yourself with high-intensity sessions leads straight to burnout or injury:
AeT training creates less physical stress and so is far less taxing on your body than high-intensity efforts
You can accumulate more quality training time. Because it’s less stressful, you can accumulate more training time in this zone without feeling wrecked, leading to bigger aerobic gains.
Faster 'bounce back'. Recovery happens faster, even from tough sessions
4. It's Your Secret Pacing Weapon
Ever gone out too fast in a race or long workout, only to crash and burn spectacularly?
Knowing your AeT gives you:
A concrete heart rate target or pace you know you can sustain
Protection against the dreaded "fly and die" scenario - you avoid tipping over into the red zone too early
Confidence in your capabilities on race day = gold
Lays the Groundwork for High-Intensity Excellence
Think of AeT training as building the biggest, strongest foundation possible.
The broader and more solid your aerobic base:
The more high-intensity work you can handle.
The faster you'll recover between hard efforts.
The higher your performance peaks can be. It’s not a case of choosing AeT or VO2max training; a great Aerobic Threshold supports and enhances your ability to hit those top-end intensities.
Simply put - If you improve your aerobic threshold, you will also see an improvement in your anaerobic threshold.
Training Your Aerobic Threshold: Simple, Not Always Easy
Once you know your AeT, training it is conceptually simple: you need to spend a good amount of time exercising at or just slightly below that specific intensity.
Zone 2 is Your Friend: Your AeT typically falls at the upper end of what’s traditionally known as Heart Rate Zone 2. This is your endurance-building zone.
Embrace Long(er), Steady(er) Efforts: Think sustained runs, cycles, rows, or brisk walks where your heart rate stays consistently in that AeT ballpark. It’s not about smashing yourself; it’s about consistent, targeted effort.
Volume is King (Initially): Building a robust aerobic base often requires a significant volume of training in this zone - something around 80% of your cardio training. This is sometimes called “base building.”
Listen to Your Body (and Your Data!): The feeling should be “comfortably challenging” – you know you’re working, but you could keep going for a good while. Your heart rate monitor becomes your best friend here, keeping you honest. We recommend using a dedicated heart rate strap for the most accurate readings - something like the Polar H10 is perfect (we use them ourselves).
Patience Pays Off: Aerobic adaptations take time. Don’t expect miracles overnight, but stick with it, and the improvements in your endurance and efficiency will come.
"Okay, I'm Sold. How Do I Find My Aerobic Threshold?"
This is where the guesswork stops and the science steps in.
While you will find various online calculators or age-based formulas for heart rate zones, these are often wildly inaccurate.
Smartwatches are also regularly off by several BPM, which can be the difference between maximising adaptations and straying into junk training territory, where you aren't really getting all the benefits, but are accumulating stress.
Remember: Your physiology is unique.
Perceived Exertion (The "Talk Test"): A rough guide is that AeT is often around an intensity where you can still hold a conversation, but it's becoming a little noticeable. However, this is very subjective and can vary day-to-day. Not a great measure.
The Gold Standard: Metabolic Testing in a Lab: The most accurate way to pinpoint your AeT is through a graded exercise test with gas exchange analysis (part of what we do in an Active Metabolic Test / VO2max assessment).
We measure your oxygen consumption (VO2) and carbon dioxide production (VCO2) breath-by-breath as you gradually increase exercise intensity on a treadmill or stationary bike.
Your AeT (identified as VT1) is the point where specific changes in your breathing pattern and gas exchange ratios occur, indicating that shift in fuel use and the very first subtle rise in lactate.
What you get: Not an estimate, but your precise heart rate, pace, and/or power output at Aerobic Threshold. In fact, we can provide all of your thresholds (Fat max, VT1, VT2, VO2 max and Heart Rate max). No more guessing if you’re in the right zone!
We look at how well your body moves and uses oxygen—across your heart, lungs, and muscles—to get a true picture of your athletic capacity. Oxygen efficiency is the engine behind everything from endurance to recovery, and it tells us a lot about how well you perform.
Ready to discover your precise Aerobic Threshold and level-up your fitness?
An Active Metabolic Test at Body Blueprints will pinpoint your unique training zones, including your critical Aerobic Threshold, giving you the power to train smarter and achieve more.
Book Your Active Metabolic Test Today and Transform Your Training!
Still have questions about Aerobic Threshold or how our tests can help you? Book a free, no-obligation discovery call with one of our experts. cal.com/bodyblueprints/discover]
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