Measuring Your Cycling FTP

On the bike, heart rate tells you what the body is going through; power tells you what it is producing. Both are useful, but only the second reads instantly, with no drift and no excuses: it is swayed neither by the heat, nor by the morning coffee, nor by the short night. What you still need is a personal reference point to place it against. That reference point is FTP.

What FTP measures

FTP stands for Functional Threshold Power. It is the highest power you can hold in a near-steady state for roughly an hour. Above it, lactate production durably outruns your capacity to absorb it and the effort collapses within minutes; below it, the body finds an equilibrium and the effort becomes a question of patience and fuel. The kinship with the anaerobic threshold AnT described in our article on heart rate zones is direct: FTP is that threshold translated into watts. The same physiological phenomenon, observed from the production side rather than from the cardiac response side. Three clarifications before going further. FTP is a power, not a speed or a pace. It does not carry over to running, where the equivalent is measured differently. An athlete can have a fine FTP and a modest running AeT: two disciplines, two training approaches, two separate reference points. FTP is a ceiling, not a target for the day. On a long mountain outing, training spends most of its time well below FTP. It serves to place your zones and to calibrate your quality sessions, not to describe a six-hour ride. FTP is measured, not calculated. Training applications offer automatic estimates based on your best power over recent weeks. Useful as they are, they assume you have actually produced a maximal effort recently. After a winter of easy rides, they simply follow the decline.

Before testing

An FTP test is only worth something if it is repeatable. The absolute value matters less than how it moves from one season to the next, and that movement can only be read if the conditions resemble each other.

• A power meter, on the bike or in the indoor trainer. Calibrate it before every test, and keep the same one from test to test: two different meters can read 5 % apart without either of them being faulty.
• Freshness. Several easy days beforehand, and above all no hard session the day before. A test taken tired measures tiredness.
• Fuel. A proper meal two to three hours before, a carbohydrate snack 45 minutes before.
• The same conditions. Same bike, same position, same clothing, same time of day, same warm-up. Write it all down in the session notes: those notes are what will make the next test comparable.

Measuring your FTP indoors

The indoor trainer removes the wind, the cars, the traffic lights and the changes of gradient. It is the most faithful environment for following progress over several years. Set up a fan: without one, heat becomes the limiting factor and the test measures your tolerance to a sauna rather than your threshold.

The ramp test

This is the simplest, and the one to pick if you have never tested. It requires no pacing at all: the machine dictates, you follow until you no longer can. You need a smart trainer able to control the resistance.

1. Warm up for 10 to 15 minutes, building progressively, with two or three short accelerations to open the legs.
2. Start the ramp at 100 W, or lower if you are a beginner.
3. Resistance increases by 20 W every minute. Hold a comfortable cadence, between 85 and 95 revolutions per minute.
4. Continue until you can no longer hold the cadence. That stopping point is the result of the test.
5. Your FTP is roughly 75 % of the power of the last complete minute.

The whole thing takes 20 to 25 minutes and demands no experience. Its weakness is well known: it draws heavily on the anaerobic pathway in the final minutes. An explosive athlete will overestimate their FTP, a diesel will underestimate it. If you are the second kind, the figure will look low compared with what you actually hold on a climb: that is not a measurement error, that is the protocol.

The 20-minute test

This is the reference protocol, the one that correlates best with a laboratory measurement. In exchange, it asks you to know how to pace an effort over time.

1. Warm up for 20 minutes: 10 minutes easy, then three one-minute accelerations at a brisk pace with a minute of recovery between each, then 5 minutes easy.
2. Ride 20 minutes at the highest power you can hold all the way to the end. Not the highest of the first five minutes.
3. Take the average power over the 20 minutes.
4. Your FTP is 95 % of that average.

The 95 % coefficient is a convention. Coaches adjust it to the athlete's profile: take off 5 % if you are enduring and not very explosive, up to 10 % if you have a large anaerobic capacity, and 7.5 % if you have no idea. Choose once and keep the same coefficient from test to test, otherwise you will be comparing different things. The difficulty of the test lies entirely in the pacing. Setting off 20 W too high is paid for in the last five minutes, and the result comes out lower than if you had started right. A good strategy is to deliberately aim a little low for the first five minutes, then step up if the sensations allow it.

The two 8-minute tests

A useful variant when 20 minutes of time-trialling feels insurmountable, or when you lack experience of pacing.

1. Same warm-up as above.
2. Ride 8 minutes flat out.
3. Recover for 10 minutes, spinning very easily.
4. Ride another 8 minutes flat out.
5. Your FTP is 90 % of the better of the two averages.

This format also says a good deal about your capacity to recover: a second block far below the first signals either too ambitious a start, or endurance still to be built. Its weakness is the same as the ramp test's, only more pronounced: eight minutes leave a large place to the anaerobic pathway, and the result tends to flatter.

What about the one-hour time trial?

That is the literal definition of FTP, and therefore the truest measurement: one hour flat out, and the average power is your FTP, with no coefficient. Almost nobody does it, because it is long, very hard, and demands about as much recovery as a race. Keep it for when you are preparing a time-trial objective, where the exercise has training value in itself.

Measuring your FTP outdoors

Outdoors, you gain in realism what you lose in control. The position is the one you actually ride in, the cooling is natural, and the movement is the one you use in the mountains. In exchange, wind, traffic and terrain can ruin a test without your noticing.

Choosing the terrain

This is the most important decision of the test, more important than the protocol itself.

• A steady 2 to 3 % climb is ideal. The gradient forces you to pedal continuously and absorbs the surges; beyond 5 %, body weight takes too large a place in the equation and comparing across seasons becomes sensitive to your changes in mass.
• No stops: no junction, no traffic light, no descending section where you stop pushing. Every second at zero watts drags the average down.
• A windless day, or a sheltered road. A constant headwind is manageable; a shifting wind is not.
• Always the same route. That is the rule that counts: your test segment becomes a measuring instrument, and an instrument does not change its unit from one year to the next.

If you have no suitable climb, a false flat or a sheltered flat road works, provided it is genuinely long and free of junctions.

The protocol

Take the 20-minute test described above and change nothing: same warm-up, same effort, same coefficient. The only difference is what you write down next to the result. Systematically record, in the session notes: the temperature, the wind, the direction of travel, the bike used, and how fresh you were. Without those lines, a 15 W difference at the next test will stay a mystery.

What distorts a test outdoors

• The wind, by far the first culprit. A test with 15 km/h of tailwind gives a fine power figure and a poor reference point.
• The heat. Above 25 °C, sustainable power drops markedly without the threshold having moved. Test in spring and autumn if you can.
• An uneven gradient. A steeper section pushes the watts up, a flatter one drops them: the average stays correct, but the effort was less efficient than a smooth one.
• Calibration. Always zero the meter, cold, just before the warm-up.
• Altitude. Above 1,500 m, maximal aerobic power falls by a few per cent. That is no problem if you always test in the same place; it is one if you compare a mountain pass with a test on the flat.

How often to retest

An FTP test is a hard session: it needs freshness before and recovery after. There is therefore nothing to gain from multiplying them. Two to three tests a year are enough: one at the start of the preparation to set the reference, one after six to eight weeks of work to check that the plan is producing something, a last one before the specific phase. Add one after a long break, an illness or an injury, when you know the reference point has moved. And look at the trend rather than the figure. An FTP up by 5 W between two tests may be progress, or it may be a day two degrees cooler with a kinder wind. Three tests across a season draw a slope; a single test says almost nothing.

What FTP changes in your training

Once the value is set, it serves three purposes. It defines your power zones. Recovery, endurance, tempo, threshold, VO2max: all of them are expressed as a percentage of FTP. An FTP that is 10 % wrong makes every one of your quality sessions wrong by the same proportion. It gives an honest reading of your long rides. On an objective lasting several hours in the mountains, the power you can hold is a fraction of FTP, and the longer the outing the smaller that fraction. Knowing your ceiling tells you how far below it you are staying, and it is that distance which decides whether you finish. It locates the work to be done. A high FTP with short endurance, and the winter will be made of long easy rides. Solid endurance under a modest FTP, and it is the threshold sessions that are missing. The number alone says nothing; set against what you hold for three hours, it says a great deal.

To place FTP against the AeT and AnT heart rate thresholds, and to build your heart rate zones, read Heart Rate Zones.