How to Improve Your VO₂ Max: What Actually Works (According to Research)

I spent years running at what felt like a productive pace. Slightly out of breath, working up a sweat, feeling like I was doing something meaningful for my health. My VO₂ max barely moved.

Then I started digging into the research, and I realized I had been training in exactly the wrong zone.

Why VO₂ Max Matters More Than Almost Any Other Metric

Before we talk about how to improve it, let's establish why you should care.

A landmark 2018 study from the Cleveland Clinic followed over 122,000 patients and found that cardiorespiratory fitness was the strongest predictor of long-term survival they measured. People with elite fitness levels had an 80% lower mortality risk compared to those with low fitness. The relationship was striking: low cardiorespiratory fitness carried comparable or greater mortality risk than smoking, diabetes, or coronary artery disease.

More recently, a 2022 analysis of over 750,000 veterans confirmed these findings. Each 1-MET increase in VO₂ max (roughly 3.5 mL/kg/min) was associated with a 13-15% reduction in mortality risk. There was no upper limit—fitness kept paying dividends well beyond what most people would consider "fit enough."

This isn't just about living longer. Higher VO₂ max is linked to better cognitive function, lower risk of dementia, improved metabolic health, and greater independence as you age. It's one of the most modifiable predictors of healthspan we have.

So how do you actually improve it?

The Training Intensity That Actually Works

Here's what surprised me most when I started reading the research: the intensity that feels productive is often the least effective for improving VO₂ max.

A 2007 study by Helgerud and colleagues compared four training protocols matched for total work over eight weeks. The results weren't even close:

Running at 70% of max heart rate (easy pace): VO₂ max improved by 0.5 mL/kg/min
Running at 85% of max heart rate (lactate threshold): VO₂ max improved by 2.4 mL/kg/min
4×4 minute intervals at 90-95% max heart rate: VO₂ max improved by 7.2 mL/kg/min

The high-intensity interval group improved nearly three times more than the threshold group, despite doing the same total amount of work. This wasn't about working harder in total—it was about working at the right intensity.

The zone that feels like "a solid workout"—moderately hard, slightly breathless, sustainable for 30-45 minutes—is what coaches call the "black hole" of training. It's hard enough to accumulate fatigue but not hard enough to trigger the cardiovascular adaptations that actually improve your ceiling.

I've written more about this in The Exact Heart Rate Zone That Improves VO₂ Max, but the short version is: Zone 4 (85-95% of max heart rate) is where the magic happens.

The Norwegian 4×4 Protocol

The most studied protocol for improving VO₂ max is deceptively simple:

Warm up for 10 minutes
Run, cycle, or row at 90-95% of your max heart rate for 4 minutes
Recover at 60-70% (easy walking or light jogging) for 3 minutes
Repeat 4 times
Cool down

That's sixteen minutes of hard work total. Research shows this protocol can improve VO₂ max by 7-10% in just six to eight weeks, even in people who are already moderately trained.

The key is actually hitting the target intensity during those four-minute blocks. You should be breathing hard enough that speaking in complete sentences becomes difficult. If you can chat comfortably, you're not going hard enough. If you can't complete all four intervals, you started too hard.

For a 35-year-old, max heart rate is approximately 189 bpm using the HUNT Fitness Study formula (211 - 0.64 × age). That makes the target zone for intervals roughly 161-180 bpm.

The 80/20 Principle (And Why It Works)

Elite endurance coaches have converged on a remarkably consistent prescription: spend about 80% of your training time at low intensity and 20% at high intensity. Almost nothing in the middle.

Dr. Stephen Seiler, who has spent decades studying elite endurance athletes, found this pattern repeatedly across Olympic-level cross-country skiers, rowers, and cyclists. The best performers in the world train this way.

A 2014 study tested this directly by assigning well-trained athletes to one of four training approaches: high-volume low-intensity, threshold training, high-intensity intervals only, or polarized (80/20). The polarized group showed the greatest improvements in VO₂ peak (+11.7%), time to exhaustion (+17.4%), and peak performance (+5.1%).

Here's why it works:

Low-intensity training (80%) builds your aerobic foundation without accumulating excessive fatigue. You can do a lot of it. You recover quickly. It improves your body's ability to utilize fat as fuel and increases capillary density in your muscles.

High-intensity training (20%) provides the signal for cardiovascular adaptation. It tells your heart to pump more blood per beat. It increases the oxygen-carrying capacity of your blood. It pushes your ceiling higher.

The middle zone does neither effectively. It's hard enough to create fatigue but not hard enough to trigger adaptation. It's the worst of both worlds.

What About Zone 2?

You've probably heard that Zone 2 training (roughly 60-70% of max heart rate) is optimal for building mitochondria. This claim has exploded in popularity through podcasts and social media.

The science is more nuanced than the headlines suggest.

A 2025 narrative review in Sports Medicine critically examined this claim and concluded that current evidence does not support Zone 2 as the optimal intensity for improving mitochondrial capacity. The researchers found that higher-intensity exercise actually activates mitochondrial signaling pathways more strongly and produces larger improvements in enzyme activity.

That doesn't mean Zone 2 is useless. It allows you to accumulate training volume without excessive fatigue. It improves fat oxidation, especially in beginners. And when combined with high-intensity work in a polarized model, it creates a solid foundation.

The key insight: Zone 2 is valuable as part of a training program, not as the entire program. If you're only doing low-intensity cardio, you're leaving significant VO₂ max improvements on the table.

A Practical Training Week

Here's what a training week might look like if you exercise four to five times per week:

Monday: 40-50 minutes easy (Zone 2). Keep your heart rate below 75% of max. This should feel almost too easy.

Wednesday: 4×4 intervals. After a warm-up, complete four 4-minute intervals at 90-95% of max heart rate with 3-minute recoveries.

Friday: 30-40 minutes easy (Zone 2).

Saturday or Sunday: Long easy session, 60-90 minutes if you have time. Still Zone 2.

That's roughly 3-4 hours of training with about 80% in Zone 2 and 20% in the high-intensity zone. Zero minutes in the black hole of Zone 3.

If you're newer to training or have less time, start with two easy sessions and one interval session per week. That's enough to see meaningful improvements.

The Lifestyle Factors That Matter

Training is the primary driver of VO₂ max improvements, but several lifestyle factors can either support or undermine your progress.

Sleep

Poor sleep quality is associated with reduced VO₂ max and worse performance during maximal exercise. Research shows that participants reporting good sleep quality presented higher VO₂ max values compared to those with altered sleep patterns.

Sleep deprivation also increases perceived exertion during exercise, meaning the same workout feels harder when you're tired. This can prevent you from hitting the intensities needed to drive adaptation.

Aim for 7-9 hours of quality sleep. If you're training seriously, prioritize sleep like you prioritize your workouts.

Body Composition

VO₂ max is expressed relative to body weight (mL/kg/min). This means that carrying excess body fat directly lowers your score—not because your cardiovascular system is worse, but because you're dividing by a larger number.

Losing excess fat while maintaining or building muscle mass can meaningfully improve your relative VO₂ max without any change in your actual cardiovascular capacity. Of course, the training you do to improve VO₂ max will also help with body composition.

Recovery

The adaptations that improve VO₂ max happen during recovery, not during the workout itself. Training provides the stimulus; rest provides the adaptation.

If you're stacking hard sessions back-to-back without adequate recovery, you'll accumulate fatigue faster than you can adapt. The 80/20 approach works partly because all that easy training gives your body time to actually respond to the hard stuff.

How Long Does It Take?

Expect to see measurable improvements in VO₂ max within four to eight weeks of consistent training, assuming you're actually hitting the right intensities during your hard sessions.

The Helgerud study showed significant gains in eight weeks. A meta-analysis of interval training studies found average improvements of 5.5 mL/kg/min with consistent training.

After the initial adaptation period, improvements tend to slow down. This is normal. Maintaining your VO₂ max requires ongoing high-intensity work—about two interval sessions per week seems to be enough for most people. Skip them for more than two to three weeks and your aerobic ceiling starts to drop.

Tracking Your Progress

Your Apple Watch estimates VO₂ max during outdoor walks, runs, and hikes—though it buries the data five taps deep in the Health app.

The watch won't update from every workout. It needs outdoor activity with GPS, adequate heart rate elevation, and relatively flat terrain. But if you're doing regular outdoor cardio, you should see updates after most sessions.

Week-to-week fluctuations are normal. Sleep, hydration, heat, and how you felt that day can all affect a single reading. What matters is the trend over months.

For a 40-year-old male, the average VO₂ max is around 38 mL/kg/min. Moving from 38 to 44 would shift you from average to above average—and based on the mortality research, would meaningfully reduce your risk of dying from any cause.

That's an achievable goal with consistent training over six to twelve months.

The Bottom Line

Improving your VO₂ max comes down to a few key principles:

Train at the right intensities. Spend most of your time going easy (Zone 2) and a smaller portion going hard (Zone 4-5). Avoid the moderate "black hole" that feels productive but isn't.
Do the hard work properly. The 4×4 protocol works. Hit 90-95% of your max heart rate during intervals. If you're not breathing hard, you're not getting the stimulus.
Be consistent. Two interval sessions per week, combined with easy aerobic work, is enough. More isn't necessarily better if it compromises recovery.
Give it time. Four to eight weeks to see initial improvements. Six to twelve months to make meaningful long-term gains.
Track your progress. Use your Apple Watch data or check where you stand compared to others your age. The trend over time matters more than any single reading.

Your VO₂ max is one of the most powerful predictors of how long and how well you'll live. And unlike your genetics, it's something you can actually change.

Want to track your VO₂ max without digging through Apple Health? VO2 Max Pro syncs with your Apple Watch data, sends you notifications when new readings come in, and translates your number into a biological age so you can see what your cardiovascular fitness actually means.