Critical Power & Functional Threshold Power (FTP)
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FTP is the highest power (watts) you can hold for roughly an hour — a practical field anchor, near the lactate threshold, that all power-based training zones are built from; critical power is its physiological cousin.
Detail
Functional Threshold Power (FTP) is the highest average power output, in watts, that can be sustained for approximately 45–60 minutes before fatigue forces a slowdown. It is "functional" because it is a field measure rather than a lab value, "threshold" because it sits near the lactate threshold (≈ LT2; see lactate-threshold), and "power" because it is measured in watts (requiring a power meter; see power-ftp). Because an all-out 60-minute test is brutal and hard to repeat, most riders perform a 20-minute maximal test and take ~95% of that average power as their FTP estimate.
FTP is the single anchor for power-based training zones: a common system (Coggan) defines seven zones as percentages of FTP, so getting FTP right keeps easy rides easy and hard intervals correctly placed (see heart-rate-zones for the heart-rate analog). The concept generalizes beyond cycling — running has an analogous threshold pace, and swimming a threshold pace per distance.
Critical Power (CP) is the underlying physiological model FTP draws on: it represents a roughly metabolically steady-state power output, derived from the hyperbolic relationship between power and how long it can be sustained across several maximal efforts. FTP is the practical, single-test approximation of this idea. Power-based thresholds are valued because watts are an objective, instantaneous output measure unaffected by the lag, drift, and day-to-day variability of heart rate.
Key facts
- FTP = highest power sustainable for ~45–60 min; near the lactate threshold (≈ LT2).
- Common estimate: 95% of a 20-minute maximal-effort average power.
- Anchors power-based zones (e.g., Coggan's seven zones as %FTP).
- Critical Power (CP) is the physiological model (power–duration hyperbola) FTP approximates.
- Watts are objective and instantaneous, unlike the lag/drift of heart rate.
Connections
- lactate-threshold — FTP sits near LT2.
- tempo-threshold-training — tempo/threshold work is performed near FTP.
- cycling — the modality FTP is most used in.
- heart-rate-zones — the heart-rate-based zone analog.
- power-ftp — the device FTP requires.
Educational content only — not medical advice. Always consult a qualified professional for individualized guidance, especially around injury, pregnancy, or medical conditions.