VO2max & Trail Running Data: Reclaiming Control
VO2max and Trail Training Data: Reclaiming Control
The obsession with data increases right along with the VO₂max numbers displayed on GPS watch screens. A dropping VO₂max, general panic. A “non-productive” status, complete self-doubt. “Bad” sleep, cancelled session. It's time to bring some calm and context back into all of this.
Statistics Are Not the Reality of Your Training
Watches like Garmin provide an enormous amount of data: estimated VO₂max, training status, fitness condition, sleep score. The problem isn't the data itself, but what we make it say.
These indicators are:
- Estimates, not direct measurements
- Based on proprietary mathematical models
- Extremely sensitive to the quality of input data
A poorly estimated max heart rate, an inaccurate optical sensor, an atypical session… and the entire analysis can be skewed.
A watch provides a statistical approximation. Your body, however, experiences a biological reality.
Your Watch's VO₂max Isn't Your Real VO₂max
Laboratory-measured VO₂max requires a test with gas exchange analysis. A watch measures neither oxygen consumed nor pulmonary exchanges. It estimates. And most importantly: a high VO₂max absolutely does not guarantee performance.
Two runners with the same VO₂max can have very different performances depending on:
- Their running economy
- Their lactate threshold speed
- Their muscle durability
- Their resistance to central fatigue
Even more counter-intuitive: you can maintain a stable VO₂max during a break… while still losing significant specific performance. A stagnating or slightly decreasing VO₂max does not equate to ineffective training.
Trail performance is multifactorial. VO₂max is just one piece of the puzzle.
The "Productive / Non-Productive" Status Is Fragile
On paper, the logic is appealing. In practice, it assumes that:
- Your max HR is accurate
- Your resting HR is reliable
- Your age and weight are up to date
- The heart rate monitor works perfectly every session
The slightest error, and the entire interpretation is biased. How many perfectly executed sessions come back as “non-productive”? Many.
It's not the session that's bad. It's the algorithm that's limited.
Personally, we never look at the “fitness condition” at the start of a session. It can confirm a feeling but never replace it.
What Science Says About GPS Watch Accuracy
Watches estimate VO₂max using models that cross-reference several variables: running speed, heart rate, and profile data (age, sex, etc.).
These models are generally reliable on a large scale. But at the individual level, accuracy varies greatly — especially depending on the quality of the heart rate signal and the context of the session.
Result: it's a good indicator for tracking a trend over time. Much less relevant for interpreting an isolated session.
In parallel, endurance physiology relies on three major pillars: VO₂max, the fraction you are able to utilize (the threshold), and your movement economy. Focusing solely on VO₂max means missing the essential.
Scientific References
- Variable Accuracy of Wearable Heart Rate Monitors during Aerobic Exercise, Gillinov, S. et al. (2017)
- Endurance exercise performance: the physiology of champions, Joyner, M.J., & Coyle, E.F. (2008)
Key Takeaways
- Watches provide estimates, not biological truths
- Observe trends over several weeks rather than daily variations
- VO₂max does not summarize trail performance
- Always cross-reference: data + sensations + life context
- Training intelligence begins with listening to yourself
Technology is a wonderful aid. But performance is built on the trails, through consistency and intelligent training.
— Antoine, Baptiste, and Etienne from TRL