Training zones guide: how to set and use intensity zones

Why zones matter

Endurance performance depends on developing multiple energy systems at different intensities. Training zones give coaches a shared language for prescribing effort: instead of saying “run at a moderate pace,” you say “hold zone 2.” That removes ambiguity for the athlete and makes training plans repeatable and comparable across sessions, weeks, and seasons.

Zones also protect against the most common amateur mistake — consistently training at medium intensity. Without clear boundaries, athletes default to a pace that feels “about right” but sits between aerobic development and threshold stimulus. The result is stagnation, excess fatigue, and eventually injury.

The problem with generic percentage-based zones

Many apps and watches set zones as fixed percentages of maximum heart rate — for example, zone 2 equals 60–70% of HR max. This approach has two fundamental problems.

First, HR max is hard to measure accurately. Age-predicted formulas (220 − age) have a standard deviation of ±10–12 beats. If your HR max estimate is wrong, every zone built on it is wrong too.

Second, the relationship between heart rate percentage and metabolic threshold varies dramatically between individuals. Two athletes with the same HR max can have lactate thresholds at 78% and 88% respectively. Applying the same percentage bands to both athletes means one is barely aerobic while the other is already above threshold.

Percentage-based models are convenient defaults, but they should be replaced with threshold-anchored zones as soon as you have real test data.

Threshold-based zones: the correct approach

A better model anchors zones to physiological thresholds — the points where your body shifts between energy systems. The two most important thresholds are:

• Aerobic threshold (LT1) — the intensity where lactate first begins to accumulate above baseline. Below this point, fat oxidation dominates and the athlete can sustain effort for hours.
• Anaerobic threshold (LT2) — the intensity where lactate accumulates faster than the body can clear it. This is the boundary between sustainable and unsustainable effort, often close to one-hour race pace.

When zones are set relative to these thresholds, they reflect what is actually happening inside the athlete — not a statistical average across populations. Tools like Raceday calculate threshold-based zones directly from test data, removing the guesswork of percentage models.

The 5-zone model from lactate testing

Lab-based lactate testing measures blood lactate concentration at progressively increasing intensities. From the resulting lactate curve, you can identify LT1 and LT2 and define five clearly bounded zones:

The 5-zone model is clean and practical. It works especially well when you have lab data to pinpoint LT1 and LT2. Each zone maps to a distinct physiological adaptation, making programming straightforward.

The 7-zone model from field testing

Not every coach has access to a lactate lab. Field tests — a timed sprint, a steady-state effort, and a maximal 12-minute run — can estimate thresholds and VO2max with reasonable accuracy.

Raceday uses this approach to generate a 7-zone model from three simple field tests. The extra zones provide finer resolution at both ends of the spectrum: a distinction between easy and recovery paces at the bottom, and separate zones for VO2max intervals, anaerobic capacity, and neuromuscular sprints at the top.

The 7-zone model is well suited to coaches who prescribe a wide variety of sessions — from long slow distance to short track repeats — and want each session type to have its own clearly defined intensity target. It also gives more nuance for athletes who race across distances, since 5K pace and 800m pace fall in different zones rather than both lumping into “above threshold.”

Using zones in practice: the 80/20 rule

Research on elite endurance athletes consistently shows a polarized intensity distribution: roughly 80% of training volume at low intensity (zones 1–2) and 20% at high intensity (zone 4 and above), with relatively little time spent in the moderate zone 3.

This polarized model works because low-intensity volume builds the aerobic engine without accumulating excessive fatigue, while high-intensity work provides the stimulus for threshold and VO2max improvements. Zone 3 — the “tempo” zone — produces training stress without the same return on adaptation, so it is used sparingly and deliberately rather than as a default intensity.

In practice, this means the majority of an athlete’s weekly hours should feel genuinely easy. Coaches who enforce accurate zone 2 boundaries — and hold athletes accountable to them — see better long-term development than those who allow intensity to creep upward.

When to recalculate zones

Zones are not permanent. As fitness improves, thresholds shift and zones need to move with them. Retesting every 8–12 weeks is a reasonable cadence for most athletes. Key moments to retest include:

• After a structured training block (base, build, or peak phase)
• When an athlete reports that prescribed paces feel too easy or too hard
• At the start of a new season or macrocycle
• After a long break from training (illness, injury, off-season)

Outdated zones lead to the same problems as poorly set zones: the athlete trains at the wrong intensity and either under-stimulates or over-reaches. Regular retesting keeps the training plan calibrated to the athlete’s current physiology, not where they were three months ago.