Functional Threshold Power: Why Cyclists Define Themselves by One Number

Ask a cyclist their FTP and you might as well be asking a runner for their marathon PR. It's identity. Training plans, group ride pacing, power zones, even bragging rights — all anchored to this one figure in watts.

But the term is thrown around more than it's understood. FTP is a useful approximation of a real physiological boundary. It's not that boundary. Knowing the difference between what FTP claims to measure and what it actually measures will make you a better test subject and a better-trained rider.

The Boundary It's Trying to Estimate

There's a line somewhere in your intensity range where lactate production starts exceeding your body's ability to clear it. Below this line, you can ride more or less indefinitely. Above it, lactate accumulates and you hit the wall — minutes for big exceedances, 20-60 minutes for small ones.

Physiologists call this maximal lactate steady state (MLSS), and measuring it properly requires a series of 30-minute efforts with lactate draws between them. It's the real boundary, and it's nearly inaccessible outside a sports science lab.

FTP is the engineering shortcut. Andy Coggan and Hunter Allen defined it as "the highest power a rider can maintain in a quasi-steady state for approximately 60 minutes." Functionally, that's close to MLSS — usually within a few watts — and it's dramatically easier to estimate in the field. You need a power meter, a course, and a willingness to suffer.

How People Actually Test FTP

There's no single correct protocol. The three most common each have tradeoffs.

The 20-minute test. Warm up, do a 5-minute all-out effort to deplete anaerobic capacity, recover 10 minutes, then time-trial for 20 minutes at the highest power you can sustain. Take your 20-minute average and multiply by 0.95. That's your estimated FTP.

This is the classic Coggan/Allen protocol. It's popular because it's short enough that most riders can complete it without requiring an entire afternoon. The 0.95 multiplier is a population average — for some riders it's closer to 0.92, for others 0.97. If you've done the test several times, you'll know which direction you drift.

The ramp test. Standard Zwift/TrainerRoad protocol. Start at an easy power and increase by a fixed amount every minute until failure. Your FTP is typically 75% of your best one-minute power at the end. Much shorter than a 20-minute test, but it over-rewards riders with strong anaerobic systems and can under-estimate FTP for diesel-type endurance riders.

Kolie Moore protocol. A long threshold test, typically 30-45 minutes at sustainable maximum. More physiologically accurate than the 20-minute test (no 0.95 adjustment needed — what you hold is your FTP), but longer and more painful.

For most recreational riders, a 20-minute test every 6-8 weeks is the right tradeoff between accuracy and practicality. Serious racers should consider a Kolie Moore test once or twice a season and use ramp tests or 8-minute tests in between.

Plug whichever test you run into the FTP calculator and save the result somewhere you'll actually reference it when planning workouts.

What the Zones Actually Mean

Coggan's seven-zone model is the standard, and almost every training platform uses some variant of it. Zones are expressed as percentages of FTP:

The zones are prescriptive. If you want to build your FTP, you do threshold work (zone 4) — typically 2x20 or 3x15 minutes at 95-105% FTP, with 5-10 minutes of easy recovery between intervals. If you want to raise your VO2 max ceiling, you do zone 5 intervals — 4-6 x 4 minutes at 106-120% FTP. If you want to build endurance, you accumulate zone 2 time — long rides of 2-5 hours at 65-75% FTP.

The mistake most recreational cyclists make is training too much zone 3 — hard enough to feel productive, not hard enough to produce real adaptation. Zone 3 feels like work, but the physiological stimulus per unit of time and recovery cost is poor compared to polarized zone 2 + zone 4/5. If you only have 4-5 hours per week to train, almost none of that should be zone 3.

Why FTP in Watts/kg Matters More Than Raw FTP

A 250-watt FTP is world-class in a 130-pound climber and moderate in a 200-pound time trialist. Power-to-weight ratio (watts/kg) is the comparison that matters for anything involving elevation. Sustained climbing is almost entirely a watts/kg contest.

General categories for trained male riders:

• 2.5-3.0 W/kg: recreational
• 3.0-3.5 W/kg: fit club rider
• 3.5-4.0 W/kg: strong club, cat 4/5 racer
• 4.0-4.5 W/kg: cat 3
• 4.5-5.5 W/kg: cat 1/2
• 5.5+ W/kg: elite / pro

Flat courses or time trials reward raw watts more than watts/kg. Heavy riders can still dominate time trials where they wouldn't touch the podium on a climbing-heavy course.

FTP Isn't a Fitness Score

Two cyclists with the same FTP can have wildly different performance profiles. One might have a massive anaerobic capacity (strong sprinter, weak climber on sustained gradients). Another might have extraordinary endurance (can hold 0.85 x FTP for 4 hours, struggles in a 30-second sprint). Both have the same FTP. Both need different training.

This is why the complete power profile — 5-second peak, 1-minute peak, 5-minute peak, 20-minute peak, FTP — tells you more than any single number. The heart rate zones give you a complementary view, especially on days when the power meter is acting up or you're training somewhere temperature affects output. And the VO2 max estimation gives you the aerobic ceiling that FTP sits under.

For context on how VO2 max and threshold intersect, the VO2 max guide walks through the relationship. And the heart rate training zones article covers the complementary zone system most riders use to cross-check power.

Updating It Over the Season

FTP isn't static. Peak fitness riders can move 20-40 watts between off-season and race season. If you're using zones from a six-month-old test, you're either undertraining (FTP has gone up) or digging yourself a fatigue hole (FTP has dropped, zones are too aggressive for your current state).

Retest at least every 6-8 weeks during a training block. More often in the first 8-12 weeks of a new program, when adaptation is fastest. Less often once you're in a maintenance phase.

The honest sign you need to retest: your threshold intervals feel easier than they should, or they feel impossible. Either way, the number has moved.

What to Do With Your Number

Once you have an accurate FTP and clean zones, the training largely writes itself: two quality sessions per week (threshold or VO2), plus zone 2 volume, plus one recovery-to-easy day. The boring weekly structure is what actually raises FTP over months. The test itself is a check-in, not the training.

Don't chase the FTP number for its own sake. A 20-watt bump from aggressive testing on a good day doesn't help if your zones become unsustainable. The useful FTP is the one that makes your threshold intervals hard-but-completable and your zone 2 rides recoverable.

References

1. Allen, H., & Coggan, A. R. (2010). Training and Racing with a Power Meter (2nd ed.). Boulder, CO: VeloPress.
2. Borszcz, F. K., et al. (2018). "Functional Threshold Power in cyclists: validity of the concept and physiological responses." International Journal of Sports Medicine, 39(10), 737–742.
3. Faude, O., et al. (2009). "Lactate threshold concepts: how valid are they?" Sports Medicine, 39(6), 469–490.
4. Jones, A. M., & Vanhatalo, A. (2017). "The 'critical power' concept: applications to sports performance with a focus on intermittent high-intensity exercise." Sports Medicine, 47(1), 65–78.
5. Seiler, S. (2010). "What is best practice for training intensity and duration distribution in endurance athletes?" International Journal of Sports Physiology and Performance, 5(3), 276–291.
6. MacInnis, M. J., & Gibala, M. J. (2017). "Physiological adaptations to interval training and the role of exercise intensity." Journal of Physiology, 595(9), 2915–2930.