Three-zone intensity model vs Coggan 7-zone

Athlete summary

Training philosophies (polarized, pyramidal, threshold, …) talk about easy / moderate / hard time shares — not Coggan’s seven power zones. Koyaro still computes Coggan zones for ride analysis, and additionally classifies every pedaling second into three coaching buckets:

Coasting (0 W) is excluded from the denominator so percentages reflect work, not descents.

How anchors are chosen

Intensity-domain anchors beat FTP fractions when you have them:

1. LT1 (easy/mid): logged lt1_power or vt1_power measurement → else FTP × 0.75.
2. LT2 (mid/hard): logged lt2_power, vt2_power, or lactate_threshold_power → else critical power (CP) when set → else FTP × 0.90.

CP is preferred over FTP for the hard boundary because it is a useful proxy near the heavy→severe transition (MLSS/RCP neighbourhood) when lab LT2/VT2 is unset — not because CP equals VT2. FTP×0.90 remains the Coggan-shaped fallback for athletes without thresholds or a CP estimate.

FTP-only athletes keep the historical polarized % path unchanged.

Why not only Coggan 7-zone?

Coggan zones are excellent for prescribing and reviewing workouts. Philosophy TID (Seiler and related work) is defined on two physiological thresholds, not seven %FTP bands. Mapping Z1–Z2 → easy, Z3 → mid, Z4+ → hard approximates the 3-zone model when anchors are FTP fractions; with true LT1/LT2 the same bucket labels track the intensity domains the literature uses.

Literature

• Seiler & colleagues — polarized / pyramidal TID and the 3-zone model anchored at VT1/LT1 and VT2/LT2. Philosophy targets, time-in-zone vs session-goal, and the P0 evidence table: Polarized 80/20 vs pyramidal vs threshold (philosophy TID) (science.polarized-80-20).
• Coggan / TrainingPeaks — 7-zone %FTP scheme (Z1–Z7) used for workout prescription and time-in-zone charts.
• Critical power as a hard-boundary proxy when LT2 is unavailable (not interchangeable with VT2).