Training Zones

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About two years ago, I started asking myself if we could define training zones in a better way. Since then, I’ve looked at just about every model out there. From a metabolic perspective, the 3-zone models tries to anchor the zones on metabolic events.  But at best those metabolic points are difficult to accurately identify. Then you have 5- and 7-zone systems. Which is best? Which is most accurate? Honestly, the best answer is: none of them. Every model has limitations.

Some systems set zones based on max heart rate. Others use lactate. Others use gas exchange, often in combination with heart rate. The critical point is not which method you use to define zones, but how you actually implement and apply them in training. Zones are simply bins from which we can assign workouts and then assess the efficacy of those workouts. They are no hard and fast physiological markers.

Take the published paper from the Aker Dæhlie Team in Norway. They laid out a slightly different zone model than what we usually see from Norway. Given the popularity of “Zone 2 training” these days, it’s worth looking closely at how proponents of any system define and use their zones.

In their framework, Zone 1 and Zone 2 overlap significantly in lactate terms: Zone 1 <1.5 mmol, Zone 2 = 1–2 mmol. The associated heart rate ranges are consistent with most published zone models. The implication here is important: lactate is highly variable and differs across individuals. Their “Zone 2” does not align with how many people think of Zone 2, it’s closer to what I would call a classic endurance training zone, not to exceed 70–75% of max heart rate. And because lactate values can swing day-to-day, they’re not a hard anchor for training zones.

The authors themselves caution against overvaluing this range. Their description of Zone 2 is telling:

“Zone 2: Semi-hard long sessions with a heart rate ~140–155 bpm and lactate up to 2 mmol/L. This training costs more than it is worth and should therefore not be prioritized. I2 can work for learning and automating technique. Cost vs. benefit must be considered. Typical duration: 1–3 hours continuous.”

Zones 3–5 in their system are close to common definitions, though their Zone 3 sits a bit lower than usual. Keep in mind, this is a long-distance focused team. World Cup skiers may operate with different zone definitions or simply do more of their quality work in Zone 4.

For context, compare this to the zone structure used in Marit Bjørgen’s training during her most successful years, as published in a detailed study. Her low-intensity zone sat at 67–75% of max heart rate, which aligns with what we’d expect. But her mid-intensity zone (MIT) didn’t start until 89–92% of max HR—leaving a gap of about 30 beats between LIT and MIT. That looks very different from the Aker Dæhlie model.

Both systems are good theoretical models, but here’s my take: endurance training above 75% of max HR usually isn’t worth the cost, especially when implemented in relatively long session. Recovery demands increase, adaptation slows, and readiness for the next hard session is delayed. In yet another commonly published model, based on maximum heart rate and lactate levels, very similar to the Aker Dæhlie model, they place Zone 2 at 72-80%, while some may place  VT1 around 80% of max HR, in my experience, that’s not where it falls for most athletes.

We like to think of zones as hard and fast. I’ve been guilty of this myself. But in reality, they’re not. Zones are simply tools to help ensure a specific adaptation. What matters is understanding the range of metabolic and neuromuscular benefits at different intensities—and then using zones to guide training toward effective outcomes.

The following chart presented by Steven Seiler based on data from the Norwegian Olympiatoppen illustrates the range of possible adaptations and the scale of the adaptation at different intensities. So it is important to understand that adaptation to training functions on a continuum and fits with my belief that these concepts of threshold(s) is fundamentally flawed.

My Advice

• Interrogate definitions. When reading or listening to others, ask what their training zones are based on. If you’re not speaking the same language, you can’t apply their ideas.
• Pick what makes sense. If you use lactate, you need frequent spot checks to understand daily variation.
• Validate new tools. Respiration, lactate, RPE, muscle oxygen, and other technologies are useful only if you confirm consistency and reliability.
• Don’t chase trends. Learn from proven methods. Assess emerging science carefully. Staying current doesn’t mean jumping on every social-media fad.
• Be clear with terminology. Scientists and coaches often use the same terms to mean very different things.
• Focus on meaningful tests. A few well-chosen tests that produce actionable data are better than endless numbers.
• Remember simplicity. For most athletes, probably everyone, percent of max heart rate is as solid a method as any for setting training zones.