Is FTP From a 20-Minute Test Sustainable for an Hour?
Functional Threshold Power (FTP) is one of the most widely used numbers in cycling. It is defined as the highest power a rider can hold in a quasi-steady state for roughly one hour without fatiguing. Most riders estimate it the same way: take the average power from a 20-minute maximal effort and multiply by 0.95.
The assumption behind that 20 minute FTP test is simple — 95 percent of your best 20-minute power should be sustainable for about 60 minutes. But is that actually true, or is it a convenient shortcut that does not hold up for every rider.
What the study tested
Researchers at the University of Zaragoza recruited 87 road cyclists and put the formula to the test. Each rider completed the standard Allen & Coggan 20-minute FTP test, then returned on a separate day to hold their calculated FTP for as long as possible — a time-to-exhaustion (TTE) trial. Riders were grouped into four performance bands based on VO2max, from recreationally trained through to professional.
The results — wide variability, even at the top
Average time to exhaustion rose with training background and fitness level, but no group came close to the assumed 60 minutes, and the spread within each group was substantial:
Recreationally trained (46 ml/min/kg VO2max) — average time to exhaustion of 35 minutes, with individual results ranging from 20 to 57 minutes
Trained (59 ml/min/kg VO2max) — average of 42 minutes, ranging from 20 to 78 minutes
Well-trained (66 ml/min/kg VO2max) — average of 47 minutes, ranging from 25 to 70 minutes
Professional (74 ml/min/kg VO2max) — average of 51 minutes, ranging from 25 to 80 minutes
Even at professional level, average sustainable time fell nine minutes short of the one-hour assumption, and some individual riders in every group could hold the power for well under half an hour.
What this means for your training
The formula is not wrong, but it is a population average dressed up as a personal number. Two riders with identical 20-minute power can have completely different tolerances for holding that power over time, shaped by training history, muscle fibre composition and pacing discipline rather than VO2max alone.
For structured training, this points to a few practical adjustments:
Treat your FTP number as a zone anchor, not a literal ceiling — use it to set training zones, but do not assume you can hold it for an hour on demand
Test time to exhaustion occasionally, not just power — a 20-minute test tells you what you can produce, not how long you can hold it
Build tolerance deliberately — sessions like double threshold days train the ability to sustain and repeat near-threshold work, which the 20-minute test does not capture
Expect variability week to week — fatigue, heat and fuelling status all move your real-world TTE more than your FTP number changes
That last point matters more than it seems. Riders who fuel properly for long threshold and tempo sessions consistently hold power longer than their carbohydrate-depleted counterparts, regardless of what their FTP test says on paper.
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