On the Swimrun Show Podcast, Mike Alexander and I discussed my newsletter. In a large way it is driven by a deep curiosity to explore topics that are interesting and/or confusing.  My ötillö worlds teamie Daniel recently asked “how important is VO₂ max for endurance performance?” It’s a great question, and the answer isn’t as straightforward as many think.

For decades, VO₂ max which is the maximum amount of oxygen your body can use during exercise expressed as the milliliters of oxygen consumed per minute per kilogram of body weight (ml/kg/min) has been seen as the gold standard of endurance potential. But as Steve Magness argues in The Science of Running - VO₂ max is not the magic number that determines success. Instead, it’s just one piece of a much bigger puzzle.

Why VO₂ Max Alone Doesn’t Predict Performance

Many elite runners have similar VO₂ max values, yet their race performances vary significantly. 

Why? Because endurance success depends on three key factors:

1. Running Economy – How efficiently you use oxygen at a given pace. Two runners with the same VO₂ max may have very different energy costs, making one much faster over longer distances.

2. Lactate Threshold (LT1 & LT2) – Your ability to sustain a high percentage of your VO₂ max without accumulating excessive fatigue. The best endurance athletes aren’t just those with a high VO₂ max—they’re the ones who can hold a high fraction of it for long periods.

3. Fatigue Resistance & Mental Toughness – Success in endurance sports often comes down to how well you handle fatigue, which isn’t measured by VO₂ max.

Does Training to Improve VO₂ Max Still Matter?

Yes, but not in isolation. The same workouts that improve VO₂ max also enhance lactate threshold, running economy, and endurance capacity, shifting your entire performance curve upward.

How to Improve VO₂ Max (And More!)

• VO₂ Max Intervals – 4 to 6 min at ~3K pace, equal recovery

• Shorter Intervals (30/30s, 60/60s) – Alternating hard/easy efforts

• Hill Repeats – 30-60s steep efforts to build power & efficiency

• Tempo & Threshold Runs – Sustainably pushing your lactate threshold

• Aerobic Base Work – High-volume, low-intensity running

When is VO₂ Max Training Most Useful?

• For Beginners – Rapid gains in aerobic capacity

• For Middle-Distance to 10K Runners – VO₂ max plays a larger role in shorter races

• After a Base Phase – Useful before transitioning to race-specific training

• For Stagnating Athletes – A short VO₂ max training block can provide a breakthrough

Your Ability to  Express Fitness

I recently watched a Zwift Academy episode on YouTube. The academy is a worldwide cycling talent identification competition that has placed riders onto World Tour teams. In this episode they tested the male cyclists with a 1-minute and 8-minute test to compare their average power and watts per kg. Note they didn’t take a lactate curve profile or gas exchange measurements. They are not interested in measures of fitness, they are interested in how an individual can express fitness in their chosen discipline. 

VO2 Max is an intensity that can be sustained for between 10 and 15 minutes. For most of us that is going to map to about your 3000m time. So how fast can you run 3000m? Here I have created a table which gives you an indicative VO2 Max span based on your time. I am personally much more interested in how I can express fitness through run performance than an abstract ml-kg-min metric.

Watch Based VO₂ Metrics

Watch based values can add to the confusion. From what I can work out, Garmin & Suunto (Firstbeat-based) provide the most reliable VO₂ max estimates. If you control the variables they can be up to ~95% accurate, or within ~3.5 mL/kg/min. But as I have neither Garmin or Suunto I can’t really confirm, nor do I guess that many people create the optimal data conditions. My Coros gives me both a VO2 Max value and race prediction times from 5km through to marathon. The two measurements must not use the same calculations as my VO2 Max number wouldn’t have a chance of running the predicted 5km time!

Race Predictions

I believe the Coros race predictions are credible as they align with my Stryd race power predictions. A 2023 study found Stryd’s Critical Power (CP) the cornerstone of its predictions, to be “highly predictive of running performance,” correlating closely with lab measures like lactate threshold and VO₂ max tests​. In fact, Stryd’s CP was equivalent to CP from standard lab models, suggesting solid physiological validity​. In addition Stryd’s Race Power Calculator will use your actual power output needed on uphills vs. flats from its library of known courses or an uploaded gpx file. It also takes environmental factors into account for temperature and humidity, and their effects on your performance. In short, Stryd personalizes predictions using your unique power vs. duration profile, course specifics, and a physiology-based fatigue model. This often yields a narrow prediction range (e.g. “±3 min”) to express uncertainty, which many runners and coaches have validated as extremely accurate.

Back to Daniel’s Question

I know Daniel uses Stryd so my advice is to focus on improving CP and w/kg though balancing stimulus across your power curve:

• Z2** Long Runs & Easy Mileage → Build aerobic base & recovery

• Z6 & Z7 Neuromuscular & Sprint Work → Boost efficiency, top-end power, larger speed-reserve

• Z3 & Z4 Threshold Runs & Tempo Work (up to CP) → Raise lactate threshold

• Z5 Intervals (above CP) → Increase Aerobic Capacity / VO₂ Max

Note I put the classic VO2 Max workouts lower down the list in terms of my training priorities. I also want to clarify my stance on Zone 2** training. 

There’s no magic in a specific "easy pace" zone. Zone 2 isn’t special, nor should it be the goal. The real objective is to go easy enough to accumulate consistent training volume. For many, that means mostly Zone 1; for others, the low end of Zone 2; and for some, the higher end of Zone 2 or even the bottom of Zone 3.

As I’ve mentioned in past newsletters, my fundamental approach remains very simple; two harder sessions per week, plus as much easy volume as I can manage. Don’t stress over false precision. Just go easy enough to recover well, build volume, and stay consistent over time.

Final Takeaway

VO₂ max is important, but it’s not the ultimate performance predictor. The best athletes are those who optimize efficiency, fatigue resistance, and sustainable power output, not just those with the highest VO₂ max.

Rather than solely chasing a bigger VO₂ max, a smarter approach is to develop all aspects of endurance across your power/pace curve. Since all metabolic systems overlap, training at different intensities strengthens the entire system, making you a more well-rounded and efficient runner. Over focusing on one adaptation means limiting your full potential.