The 80/20 zone system
80/20 Endurance (Matt Fitzgerald and David Warden) sets zones as a percentage of lactate threshold heart rate and of threshold speed. The two “gray zones”, X and Y, sit between the main zones and are deliberately avoided so easy running stays easy and hard running is properly hard.
| Zone | HR, % of LTHR | Speed, % of threshold | Purpose |
|---|---|---|---|
| 1 | 72–81 % | 60–76 % | Easy / recovery |
| 2 | 81–90 % | 76–87 % | Aerobic — most of your running |
| X | 90–95 % | 87–93 % | Gray zone — avoid |
| 3 | 95–100 % | 93–100 % | Threshold |
| Y | 100–102 % | 100–102 % | Gray zone — avoid |
| 4 | 102–105 % | 102–115 % | VO2max intervals |
| 5 | 105+ % | 115+ % | Speed / sprints |
Source: 80/20 Endurance intensity guidelines for running. Pace from speed: pace = threshold pace ÷ (speed % / 100).
What 80/20 means in practice
About 80 % of weekly training time goes in Zones 1–2 and about 20 % in Zones 3–5. For a runner training five hours a week that is roughly four hours easy and one hour of threshold, interval and speed work — including the warm-ups and cool-downs of those sessions at easy effort.
Low intensity
Zones 1–2: easy runs, long runs, recovery. You should be able to talk in full sentences.
Moderate & high
Zones 3–5: threshold runs, VO2max intervals, strides and hill sprints.
Related: heart rate zones from max HR, Zone 2 calculator and Norwegian singles.
Last reviewed: September 2026 · Health disclaimer