FTP: how to test it and build your power zones

Almost every structured cycling workout is prescribed as a percentage of one number: your FTP. Get it roughly right and your zones line up with your physiology; get it wrong and every session is either too easy or quietly digging you into a hole. Here's how to find it and turn it into usable zones.

What FTP actually measures

Functional Threshold Power is the highest power you can hold in a quasi-steady state before fatigue climbs sharply — in practice, roughly the average power you could sustain for about an hour. It's a field-friendly proxy for your lactate threshold, the intensity where lactate production starts to outrun clearance. It is not your one-hour max on a good day so much as a stable anchor for setting zones.

How to test it

You don't need a lab. The three common field tests, from most to least demanding:

• 20-minute test: warm up, do one all-out but evenly paced 20-minute effort, then take 95% of your average power. The classic — accurate, but the 20-minute effort is genuinely hard to pace.
• Ramp test: power steps up every minute until you can't hold on; FTP is about 75% of your best 1-minute power. Shorter and easier to pace, but tends to over-rate strong sprinters and under-rate diesel engines.
• 8-minute test: two 8-minute efforts, take ~90% of the average. A middle ground.

Whichever you pick, keep the protocol the same every time. A consistent, slightly imperfect test you repeat is far more useful than switching methods and comparing numbers that aren't measuring the same thing. You can also let software estimate FTP from your recent hard rides — handy, but confirm it with a real test a few times a year.

Turn FTP into your seven zones

The standard Coggan model splits training into seven zones as a percentage of FTP. This is what most platforms, including Intervals.icu, use by default:

• Zone 1 — Active recovery: under 55% FTP. Spinning, genuinely easy.
• Zone 2 — Endurance: 56–75%. The aerobic base that most of your hours should sit in.
• Zone 3 — Tempo: 76–90%. 'Comfortably hard', useful but easy to overuse.
• Zone 4 — Threshold: 91–105%. Right around FTP — the classic 2×20 territory.
• Zone 5 — VO2max: 106–120%. 3–5 minute efforts that lift your ceiling.
• Zone 6 — Anaerobic: 121–150%. Short, sharp 30s–2min repeats.
• Zone 7 — Neuromuscular: 150%+. Sprints, measured in seconds.

How often to retest

Every 4–6 weeks of consistent training is a sensible cadence, plus once after any long break. If your threshold sessions suddenly feel easy — or brutally hard — that's a sign your FTP has moved and your zones are stale. Testing too often just costs you a hard session for little new information.

A common mistake to avoid

Don't set your FTP to the number you wish you had. An inflated FTP makes every 'threshold' session an over-threshold session; you'll accumulate fatigue faster than you adapt, and your Form will tell the story a couple of weeks later. If anything, err slightly conservative — it's easier to add intensity than to dig out of a hole.

Once your zones are dialled in, the harder question is which sessions to actually do this week given your fatigue and your race. That's where an adaptive coach earns its keep: Upform reads your Intervals.icu data and prescribes sessions in the right zones at the right time, then adjusts as your FTP and Form change.