If you’re reading this, there’s a good chance you already know your VO₂ max.
You’ve seen it on your Garmin, Oura, or lab report. You’ve watched it tick up… or stubbornly refuse to budge. And at some point, you were probably told the same thing everyone is told:
“Just run more (build a bigger aerobic base).”
“Add intervals.”
“Increase volume.”
That advice isn’t wrong — it’s just incomplete (I feel).
And for a lot of endurance athletes I work with, especially those preparing for high-altitude objectives, it’s actively unhelpful.
Because most people don’t have a mileage problem.
They have an efficiency problem.
And since most people also have a time problem, I wrote this article to explain how to increase VO₂ max without adding more miles — by identifying what’s actually limiting oxygen delivery and utilization, and training that instead – to be more time-efficient for the work you put in.
The Mistake Most Athletes Make About VO₂ Max
Starting for the top here: VO₂ max is often treated like a single trait — a number you either have or don’t.
In reality, it’s an output metric that sits at the end of a long physiological chain:
- Ventilation (how you breathe)
- Gas exchange (how oxygen moves into blood)
- Cardiac output (how much blood your heart can move)
- Blood oxygen carrying capacity
- Peripheral extraction (how muscles actually use oxygen)
Most training programs assume the limiter is the heart/cardiovascular system.
So we pile on:
- More aerobic base
- More tempo
- More intervals
- More mileage
You know, the things to improve our oxygen uptake capacity (and lactate buffering capacity). And that works – for a while.
But oftentimes, VO₂ max plateaus — not because the engine isn’t strong enough, but because airflow, control, or tolerance upstream is holding everything back.
Running more doesn’t fix a bottleneck. It actually makes it – and you – suffer more 🙂
Why “Just Run More” Often Fails, Especially After 40 or 50
Earlier in life, you can get away with inefficient systems.
You recover faster. You tolerate stress better (maybe…). You muscle through suboptimal mechanics.
As we age, the margins tighten.
What I see repeatedly in 50+ endurance athletes is this pattern:
- Strong discipline
- Consistent training history
- Plenty of aerobic work
- But poor breathing efficiency
- Low CO₂ tolerance
- Overactive stress response under load
And here’s the key insight:
VO₂ max is limited just as often by how you breathe as by how hard you train.
If ventilation is inefficient, oxygen never reaches its potential downstream — no matter how many miles you log.
What Actually Limits VO₂ Max (Beyond Mileage)
Let’s break this down practically. In my coaching experience, I’ve seen issues with:
1. Breathing Mechanics
Most adults breathe:
- Too fast
- Too shallow
- Too chest-dominant
- With poor nasal function
This increases the cost of breathing.
At altitude — where air pressure is lower — that cost rises even further. Your respiratory muscles must work harder just to move the same volume of air (and hopefully, for starters, you are actually engaging your respiratory muscles – the ones actually designed to do your breathing)
If your diaphragm is undertrained, your body compensates by:
- Increasing breathing rate
- Triggering stress responses
- Burning energy that should go to locomotion
Training more miles doesn’t fix this….training the breathing muscles does.
2. CO₂ Tolerance (The Most Ignored Limiter)
This is the quiet one. Most people think breathlessness is caused by “not enough oxygen.”
….It isn’t. It’s driven primarily by carbon dioxide accumulation. (with the exception of high altitude scenarios, where BOTH Oxygen and CO2 may cause chemoreceptor signaling)
Low CO₂ tolerance means:
- You feel uncomfortable earlier
- You breathe harder sooner
- You exit efficient aerobic work prematurely
This artificially caps VO₂ max expression — especially during sustained or high-altitude efforts.
Raising CO₂ tolerance allows:
- Slower breathing at higher outputs
- Better oxygen delivery
- Lower perceived exertion (RPE) at the same workload (which is tied to more endurance)
Again: more mileage doesn’t target this directly.
3. Nervous System Inefficiency
VO₂ max isn’t just a mechanical system. It’s regulated.
If your nervous system interprets stress too early, it will:
- Increase ventilation
- Increase heart rate
- Reduce efficiency
This is why two athletes with identical VO₂ max numbers can perform very differently.
One stays calm under load. The other burns matches immediately.
Training intensity without nervous system control often worsens this problem.
How to Increase VO₂ Max Without Running More Miles
So what actually works?
Here’s the reframe:
VO₂ max improves fastest when you remove the primary limiter — not when you pile more work onto the system.
Below are the most effective, non-mileage levers.
1. Improve Ventilatory Efficiency
This is foundational.
- In our SUMMIT process, we identify your poor breathing habits in the S, Survey. Then we U – un-learn these bad habits.
Training nasal breathing, diaphragmatic control, and reduced breathing volume lowers the oxygen cost of movement.
When ventilation becomes cheaper:
- More oxygen is available for muscles
- Heart rate stabilizes
- VO₂ max expression improves without added load
This matters enormously at altitude, where every inefficiency is magnified.
2. Train Respiratory Muscles Directly
This is the first M in SUMMIT – Muscle strength-training.
Respiratory muscles fatigue, just like quads or calves. And studies show that targeted respiratory muscle training can:
- Improve oxygen saturation at altitude
- Reduce perceived breathlessness
- Improve endurance performance without additional mileage
If breathing is the limiter, strengthening the breathing muscles is not optional.
3. Increase CO₂ Tolerance Intelligently
This doesn’t mean reckless breath-holding.
It means controlled exposure to:
- Elevated CO₂
- Mild hypoxia
- While maintaining calm, controlled breathing
This shifts chemoreceptor sensitivity and delays the ventilatory threshold — one of the strongest predictors of endurance performance.
In practical terms:
- You stay aerobic longer
- You access higher outputs without panic breathing
- VO₂ max becomes usable, not just theoretical
4. Use Intensity More Precisely (Not More Often)
Intervals work — when they’re appropriate.
But adding intervals on top of inefficient systems often just reinforces dysfunction.
When breathing and nervous system efficiency improve first:
- Intervals become more productive
- Recovery improves
- VO₂ max adaptations happen with less total stress
This is especially important for older athletes balancing recovery and longevity.
Why Diagnostics Matter Before More Training
This is where most programs fail. They prescribe before they assess.
At Recal, we use diagnostics (the S – survey – in our SUMMIT process) to identify:
- Whether ventilation, CO₂ tolerance, or mechanics are the primary limiter
- Whether endurance is capped by physiology or control
- Where training effort will actually produce adaptation
Without diagnosis, adding volume is just guessing.
With diagnosis:
- Training becomes targeted
- VO₂ max improves with less total work
- Confidence replaces constant second-guessing
A Word on Weight Loss and VO₂ Max
Yes — VO₂ max is expressed relative to body weight.
And yes, losing excess weight can improve the number.
But that doesn’t mean it improves performance or safety.
I’ve seen plenty of lighter athletes struggle at altitude because:
- Their breathing is inefficient
- Their CO₂ tolerance is poor
- Their nervous system is overreactive
Chasing the number without addressing the system is a dead end.
Why This Matters Even More at Altitude
At altitude:
- Oxygen pressure drops
- Respiratory workload increases
- Inefficiencies compound rapidly
You don’t get to “fake” VO₂ max up high.
What you bring with you — breathing efficiency, tolerance, control — determines how well you adapt and how safely you move.
This is why increasing VO₂ max without more miles isn’t just about performance.
It’s about margin.
Frequently Asked Questions
How can I increase my VO₂ max fast?
By removing the biggest limiter – and most underlooked element – first. For many athletes, that’s breathing efficiency and CO₂ tolerance — not necessarily more mileage.
What is a good VO₂ max by age?
It depends on sex, sport, and context. I cover this in detail in What Is a Good VO₂ Max for Your Age? (And How to Beat It).
Does losing weight improve VO₂ max?
It can improve the number, but not necessarily performance or altitude tolerance.
Why is my VO₂ max so poor?
Often because ventilation, tolerance, or nervous system regulation is limiting oxygen delivery — not because you lack fitness.
Is a VO₂ max of 40 bad?
Not inherently. Context matters. Many successful high-altitude climbers operate well below elite VO₂ max values due to superior efficiency.
The Takeaway
If you’re short on time, long on discipline, and tired of chasing numbers that won’t move:
- Stop adding miles.
- Start identifying what’s actually limiting you (take the Recal Breath Index)
When breathing improves, VO₂ max follows — often faster, and with far less wear and tear.
That’s not a shortcut. That’s efficiency.