When it comes to running long-distance events like the marathon, every athlete wants to know: “How fast can I go?”
Thanks to advancements in wearables and performance testing, two metrics often dominate the conversation—VO₂ Max and Threshold (also called lactate threshold or functional threshold pace/power). But what’s the difference between them, and which one actually matters when it comes to predicting race-day performance?
Let’s break it down…
VO₂ Max vs. Threshold: What’s the Difference?
These two metrics both speak to your aerobic fitness, but they measure very different things:
| Metric | VO₂ Max | Threshold (Lactate/Functional) |
| Definition | The maximum amount of oxygen your body can use during intense exercise (ml/kg/min) | The highest pace or power you can sustain for ~45-60 without fatigue building up rapidly |
| Think of it as | The size of your engine | Your sustainable race speed |
| Tested using | VO₂ Max lab test or estimates via GPS/HR/Power watches | Lab lactate tests/field testing or estimated via training data (e.g. Stryd, TrainingPeaks, WKO5) |
| Trainability | Partially limited by genetics | Highly responsive to consistent training |
Which Metric Predicts Marathon Performance More Accurately?
This might surprise some runners:
Threshold is a better predictor of marathon performance than VO₂ Max.
Here’s why:
- VO₂ Max tells you how much oxygen your body can process—it’s an indicator of potential.
- But threshold tells you how efficiently your body can operate at submaximal effort, which is exactly what you need for a marathon and ultra-distance running.
A marathon isn’t run at your VO₂ Max. It’s typically run at 75–85% of it (higher for competitive and elite athletes). So, knowing your VO₂ Max doesn’t tell you how long you can hold a fast pace before falling apart.
Real-World Example
Let’s say you have two runners:
Runner A
- VO₂ Max: 65 ml/kg/min
- Threshold Pace: 4:30 min/km
- Likely Marathon Time: ~3:10
Runner B
- VO₂ Max: 65 ml/kg/min
- Threshold Pace: 5:00 min/km
- Likely Marathon Time: ~3:30
They have the same VO₂ Max, but Runner A can sustain a faster pace for longer. That’s the power of threshold fitness and is fundamental to endurance training.
Why VO₂ Max Can Be Misleading
Many runners chase VO₂ Max numbers on their running watches as a badge of honour, but this number on its own doesn’t guarantee race-day success.
- You can have a high VO₂ Max and still blow up halfway through a marathon.
- VO₂ Max doesn’t account for fatigue resistance, fuelling strategy, or mental strength.
- Most importantly, it doesn’t reflect how well-trained you are to run at race pace.
What Should You Focus On?
If you’re training for a marathon or ultra-distance race:
VO₂ Max is your engine size– great to have, but only part of the story.
Threshold is your gear system and fuel efficiency– it tells you how fast you can go without breaking down.
To improve your marathon performance (using specific sessions at the appropriate time in the training cycle):
- Train to increase your threshold pace or power (using specific sessions)
- Use tools like Stryd or lactate testing to measure progress.
- Prioritise sustainable endurance over maximal bursts.
- Build long runs at or just below threshold to improve fatigue resistance.
Final Takeaway
In endurance running, VO₂ Max sets the potential, Threshold shows the reality.
You don’t win marathons with a big engine—you win them by using your engine smartly and efficiently over 42.2 kilometres.
If you’re serious about improving your marathon or ultra-distance performance, focus on structured, personalised training that develops your threshold, your race-specific endurance, and your ability to perform under fatigue.
Need Help With That?
At A-Team Coaching, we analyse your VO₂ Max, power zones, threshold metrics, and real-world training data to build you a performance-driven plan—backed by science and delivered by our coaches!
Want expert help turning your metrics into a marathon PB? Sign up with A-Team Coaching