Power Zones — Why Coggan's Classic Model Isn't Always Optimal
Coggan's model — 6 or 7 zones calculated as a percentage of FTP — is everywhere: Zwift, TrainerRoad, this site. It's a good default because it works for the average amateur without extra testing. The problem is the word "average" — your physiology doesn't have to be average. We look at where rigid FTP percentages break down and what to do when your zones just don't seem to fit.
Where the percentages come from, and why it's a simplification
The classic split (covered in more depth in our intro to Coggan's 7 zones) assumes that once you know FTP, you know everything — Z2 is 56–75% of FTP, threshold is 91–105%, VO2max is 106–120%, and so on. It works because FTP itself is already an aggregate of several physiological processes at once. But that's exactly why two riders with identical FTP can have completely different profiles: one handles long threshold intervals well, the other "blows up" after 8 minutes, despite the same number on the head unit.
Where rigid boundaries fail hardest
Riders with an extreme power profile (sprinters, climbers)
Coggan's model assumes a smooth, fairly symmetrical power curve. A sprinter with very high anaerobic capacity and a climber with dominant aerobic endurance have power curves of completely different shapes — and zones calculated from a single point (FTP) don't capture that difference at all. More on this mechanism in our article on VLaMax and the sprint-vs-endurance tradeoff.
FTP drift during the season
FTP isn't a fixed physical constant — it shifts with form, fatigue, even time of day. Zones calculated from a stale FTP (tested once every 8–12 weeks) systematically lie in one direction or another, especially mid-build, when FTP is genuinely rising week over week.
The Z2/Z3 (tempo) boundary is often arbitrary
The physiological difference between the top of Z2 and the bottom of Z3 is, in practice, a continuum — for many riders the aerobic threshold (first metabolic threshold) falls clearly below or above the "paper" 75% FTP line. Effect: a session planned as "easy base" can land in a zone that builds fatigue faster than intended.
Alternatives and refinements to the model
| Approach | What it improves | Cost |
|---|---|---|
| Heart rate zones alongside power | Reveals the gap between mechanical and physiological load | Requires tracking Efficiency Factor |
| More frequent FTP retests | Zones don't go stale mid-block | More frequent ramp tests |
| VLaMax / lactate threshold model (INSCYD-style) | Captures your individual anaerobic vs aerobic profile | Needs lab testing or field protocols |
| Subjective calibration (RPE + data) | Catches days when the "paper" zone doesn't match how it feels | Requires experience reading your own fatigue |
When it actually matters
For an amateur training 4–6 hours a week with a general goal of "get stronger," the imperfections of Coggan's model rarely decide the outcome — training consistency matters more than zone-boundary precision. It's worth digging into when: you're building a plan around a specific race with a clear demand profile (sprint finish, long road race), or you regularly finish "threshold" sessions noticeably easier or harder than they should feel, measured by perceived fatigue against TSS.
Track zones alongside heart rate and TSS
WattLog.pro calculates power zones from your FTP, but also shows heart rate and Efficiency Factor on the same chart — so you notice faster when a "paper" zone drifts from what you actually feel.
Try WattLog.pro for free →Coggan's model stays the default starting point for good reason — it's simple and works for most people. But "most people" doesn't mean "you." If you have an unusual power profile, or regularly feel a gap between the zone on paper and the effort in your legs, it's worth reaching for an extra signal — heart rate, EF, or a more detailed physiological model.
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