CoachingAnswer

WHAT IS FUNCTIONAL THRESHOLD POWER, PHYSIOLOGICALLY?

By Anthony WalshRoadman CyclingUpdated 10 July 2026

ANSWER

Functional Threshold Power is the highest power output a rider can sustain in a quasi-steady state for approximately one hour, developed by Dr Andrew Coggan as a practical field proxy for lactate threshold — the point where lactate production begins to outpace clearance. It's typically estimated from a 20-minute maximal test (multiplied by 0.95) rather than a genuine hour-long effort, which introduces a margin of error most riders never account for.

KEY TAKEAWAYS

FTP approximates lactate threshold — the point where blood lactate accumulates faster than it clears.
The 20-minute test protocol (×0.95) is a practical estimate, not a lab-verified figure.
FTP is a proxy, not a fixed biological constant — it shifts with fatigue, fuelling, and pacing.
Ramp tests estimate FTP differently again, and the three methods don't always agree.

WHO THIS IS FOR

IS THIS YOU?

The data-curious rider who wants to understand the number, not just use it

You use FTP to set your zones but have never understood what's actually being measured or why the test protocols differ.

The rider getting inconsistent FTP results across test types

Your ramp test, 20-minute test and real-world hour effort keep disagreeing, and you want to understand why before trusting any single number.

THE ROADMAN VIEW

FTP gets treated like a fixed biological fact when it's really a practical estimate of something harder to measure directly — the power output at which lactate accumulation tips from manageable to overwhelming. Dr Andrew Coggan built the concept specifically because lab lactate testing wasn't accessible to most cyclists. The 20-minute test with a 5% discount is a clever workaround, not a precise measurement.

That distinction matters because riders treat a single FTP test result as gospel and build training zones on it without questioning the conditions. A 20-minute test done on tired legs, in heat, on a bad day, produces a number that's real for that day but not necessarily representative of your true threshold. Testing methodology and testing conditions matter as much as the result itself.

The practical takeaway isn't to distrust FTP — it's to treat it as a working estimate that should be periodically checked against how your training actually feels. If every threshold session feels far harder or easier than it should at your current FTP, the number is probably stale, regardless of what the test said six weeks ago.

EXPERT EVIDENCE

WHAT THE EXPERTS SAY

Dr Andrew CogganExercise physiologist, co-developer of the power-based training zone model
FTP was designed as a practical, field-testable proxy for lactate threshold, not a replacement for direct physiological measurement. The 20-minute test protocol trades some precision for accessibility — most riders don't have lab access, but almost anyone can do a hard 20-minute effort.

PRACTICAL APPLICATION

DO THIS WEEK

Choose one test protocol and stay consistent
Whether you use a 20-minute test, a ramp test, or a genuine hour effort, stick with the same method across retests so you're comparing like with like rather than chasing noise between different protocols.
Test under representative conditions
Test when rested, fuelled, and not amid a heavy training block. A test done on fatigued legs produces a number that reflects that day's tiredness more than your actual threshold.
Cross-check your number against how training feels
If threshold intervals at your stated FTP consistently feel far too easy or far too hard after a few weeks, treat that as a signal the number needs retesting rather than pushing through a mismatched zone.

COMMON MISTAKES

WHAT CYCLISTS GET WRONG

MISTAKETreating a single FTP test result as a permanent, precise figure.
FIXRecognise FTP as an estimate that drifts with fitness, fatigue and testing conditions. Retest every 6-8 weeks, and sooner if training consistently feels mismatched to your zones.
MISTAKESwitching test protocols and being confused when numbers don't match.
FIXRamp tests, 20-minute tests and hour-long efforts estimate the same underlying concept differently and will rarely produce identical numbers. Pick one method and track trends within it.
MISTAKETesting FTP during a heavy fatigue week.
FIXSchedule tests at the end of a lighter or taper week when you're reasonably fresh, so the result reflects genuine fitness rather than accumulated tiredness.

FAQ

FREQUENTLY ASKED QUESTIONS

Is FTP the same as lactate threshold?

Not exactly — FTP is a practical power-based proxy for lactate threshold, designed to be field-testable without a lab. It correlates closely with lactate threshold for most trained cyclists, but it's an estimate of the underlying physiology, not a direct measurement of blood lactate.

Why does my ramp test FTP differ from my 20-minute test FTP?

The two protocols stress different systems and use different estimation formulas. A ramp test tends to be influenced more by anaerobic capacity and VO2max, while a 20-minute test more directly reflects sustainable threshold power. Neither is 'wrong' — they're estimating the same concept from different angles.

How accurate is the 20-minute FTP test?

Reasonably accurate for most trained riders when pacing is even and conditions are representative, but it can be off by 5-10% for riders with unusual anaerobic-to-aerobic profiles, or when pacing is poor. Treat it as a strong estimate, not a lab-grade measurement.