What is Seiler’s three-zone model?
The three-zone model divides endurance intensity using two physiological thresholds. Zone 1 is below the first threshold, zone 2 is between the first and second, and zone 3 is above the second. In Zonometry, we call those regions easy, moderate, and hard. [2]
This explains a common confusion: “Zone 2 training” can mean different things in different systems. The second of five watch zones is not automatically the second of three physiological regions. Before comparing a workout with a training recommendation, identify the model and its boundaries.
Watch Seiler explain the framework
In Training Intensity Zones: general rules and importance of individual testing, Stephen Seiler distinguishes the physiological anchors of a zone system from the practical subdivisions coaches use. He then explains why individual measurements matter.
Why have five zones if there are two thresholds?
Three regions answer a physiological question: on which side of the two thresholds does this effort sit? More zones can answer a coaching question: how do we describe different kinds of work within those broad regions? A subdivided vocabulary can be useful without every division representing a separate physiological transition.
Seiler’s presentation uses the Norwegian framework to illustrate this distinction. Extra subdivisions provide practical detail; the simpler three-region model is useful when studying the overall distribution of training. His athlete examples also show why population estimates and fixed lactate values can describe an individual poorly. [1]
A practical five-to-three grouping
The practical consequence is that a five-zone chart and a three-zone chart cannot be compared by matching their numbers. Nor can all five-zone systems be treated as interchangeable. The Apple Watch guide explains how Zonometry groups Apple’s zones.
Thresholds are personal measurements
The model is often described using lactate thresholds, LT1 and LT2, or ventilatory thresholds, VT1 and VT2. These are ways of assessing changes in the body’s response as exercise intensity increases. A heart rate associated with a threshold is useful because it turns a laboratory observation into something an athlete can monitor during training. It is still tied to the method, conditions, and exercise mode used to establish it. [2]
A watch estimate is a useful starting point. An exercise test gives you a more personal reference, which you can enter as a custom boundary in Zonometry.
Consider two hypothetical runners with an identical maximum heart rate. If their first thresholds occur at different heart rates, applying the same percentage-based boundary to both can label the same relative physiological effort differently. Maximum heart rate alone cannot tell you where both thresholds fall.
Where moderate training fits
“Threshold” is sometimes used as a short label for the middle zone, but that can be misleading. The whole region between the first and second thresholds is broader than work performed right near the second threshold. “Moderate” is the label Zonometry uses to keep that distinction clearer.
Moderate work has a place in endurance training. The 2015 review describes successful athletes who spend a meaningful share of their training between the two thresholds. Zonometry makes that time easy to spot, whether it comes from a planned tempo run or an easy day that became harder than expected. [2]
How the zones connect to 80/20
Once you know your zones, you can look at the balance between them. An 80/20 approach puts most of your training at an easy intensity and a smaller share at higher intensity. The resulting chart depends on whether you count whole workouts or individual minutes.
For example, a hard workout can include a long easy warmup and recoveries. Categorizing the workout as hard gives one answer; adding every heart-rate minute to its corresponding region gives another. Neither calculation changes the workout you performed. Our interactive counting example shows how the two calculations differ.
How to apply the model when reading your data
- Name the system. Ask whether a zone number refers to Apple’s five zones or the physiological three-zone model.
- Identify the boundaries. Know whether they came from an automatic estimate, a manual choice, or an individual assessment.
- Check the counting method. Session percentages and heart-rate-time percentages are not interchangeable.
- Keep the time window in view. A single interval day can look very different from the month around it.
Changing a zone boundary can change the displayed mix even when the recorded training stays the same. Keep the settings consistent when comparing weeks.
Sources
- Stephen Seiler. Training Intensity Zones: general rules and importance of individual testing. Video presentation.
- Stöggl TL, Sperlich B (2015). The training intensity distribution among well-trained and elite endurance athletes. Frontiers in Physiology 6:295. Definitions, measurement methods, and review of training patterns. Our detailed paper notes.
- Seiler S, Tønnessen E (2009). Intervals, Thresholds, and Long Slow Distance: the Role of Intensity and Duration in Endurance Training. Sportscience 13:32–53. Further reading on practical and physiological zone systems.