The WattPlan Podcast · Episode 38 · 9 min
Has my FTP gone up? How WattPlan decides, and why it asks
Next episodes: What is FTP, and is your test telling the truth? · What is W prime, and why do I crack twenty watts over threshold? · Why is my power lower indoors?
Read the transcript
James. Hello, and welcome to the WattPlan Podcast. I'm James. Between family life, work and the odd podium, I'm building WattPlan and reading sports science long after any sensible person would have gone to bed. This week, a ride that felt enormous and an app that said nothing about it. How does WattPlan decide your FTP has gone up, and why does it ask instead of just changing it? Lyra's here, our AI research voice, and the studies are linked in the show notes.
Lyra. The rule is short. WattPlan takes your best twenty minutes from a ride and multiplies by 0.95. If that's at least three percent above your current FTP, it shows you the number and asks, at the end of a structured workout in the player, or on the Today screen for any recent ride. It never changes your FTP by itself, and an ordinary ride never talks it down.
James. Wait, it never lowers it? So if I have a shocker of a ride, my FTP just sits there looking pretty?
Lyra. From an ordinary ride, yes, and that's deliberate. One bad day is sleep, heat or a hard week at work, not lost fitness. A test is different. Finish one of the FTP tests in the player and it offers whatever the test says, up or down, and you still choose.
James. Okay, that I can live with. Why 0.95? I've used it for years and never asked where it comes from.
Lyra. FTP is meant to be what you could hold for a full hour, and twenty minutes is the shortcut. We looked at two papers for this episode, and the first tests that shortcut directly. MacInnis and colleagues, in the International Journal of Sports Physiology and Performance, had eight trained male cyclists ride two twenty minute time trials and one full hour. [1]
James. And did twenty minutes predict the hour?
Lyra. It ranked them very well, and it was very repeatable, their two attempts came out about two watts apart. But for the hour they held about 90 percent of their twenty minute power, not 95. So 0.95 is a convention. For some riders it fits, and for others it's a little flattering.
James. Flattering. So the number it offers me could be too generous.
Lyra. It could, which is one reason it asks. The other is the three percent. Below that, you're inside the noise of a cool room or a good night's sleep, and every zone in your plan would shift for nothing. A change has to be big enough to be worth acting on.
James. But here's my problem. Last week I did a long sweet spot session, felt like a hero, and got nothing. Surely that ride should have counted?
Lyra. It did count, it just didn't clear the bar. Sweet spot is ridden below your FTP. Take 95 percent of your best twenty minutes from a sweet spot ride and you'll usually land below your current number, so there's nothing to offer. Feeling heroic and being above threshold aren't the same thing.
James. Fair. Brutal, but fair. So the hero rides that count are threshold and above.
Lyra. Or any ride where you held something hard for twenty minutes. It looks at every structured workout of at least twenty minutes, so a hard twenty minute block inside a longer session counts too.
James. Is that all it's watching for?
Lyra. No. And sweet spot goes completely quiet on the second check, which is the more interesting one. After a player ride, WattPlan also estimates your critical power and W prime from the shape of your power curve. Critical power is roughly the effort you could hold for a long time. W prime is the fixed amount of work you've got above it.
James. Where does that idea come from? It sounds very modern.
Lyra. It's older than most of us. The second paper is Monod and Scherrer, in Ergonomics in 1965. They defined the critical power of a working muscle group from the most work it could do and how long it could keep doing it. That two parameter idea is still what sits underneath the model today. [2]
James. And it gets that from one ride?
Lyra. Not from one ride on its own. It merges your best efforts from about one to twenty minutes in this ride with the last ninety days, and fits a line through them. A shaky fit is thrown away rather than shown. It asks when critical power moves by five percent or W prime by ten.
James. Why would sweet spot break that, though? It's still hard work.
Lyra. Because a curve needs efforts at genuinely different intensities. A steady session is one intensity repeated, and a line through that looks confident and means nothing. So it checks first. Your best minute or two has to be clearly above your best ten or twenty, and something short has to go above your FTP. Otherwise it skips the ride.
James. Great sessions for training, useless for measuring.
Lyra. That's a fair way to say it. VO2max sessions, threshold work and tests are what it learns from.
James. Okay, practical one. Most of my riding's outside and lands from my head unit. Does any of this happen for those rides?
Lyra. Yes, as long as the ride comes in with its full power data. A Strava, Garmin or Wahoo ride with second by second power keeps its best twenty minutes, and the Today screen checks your five most recent. If one clears three percent, you'll see FTP looks higher, with the ride it came from. One catch. A flat-out group ride can put a big number up, so ask whether you could hold it on your own for an hour.
James. So if I'm new to training and that box pops up, do I just say yes?
Lyra. If you're new to structured training, say yes when it matches how things have felt. Sessions finishing with something left, intervals that used to hurt now feeling steady. If you're not sure, keep your number and let the next few sessions decide. Too high is the expensive mistake, because you'll spend weeks failing intervals.
James. And if you train with power and you've got a new power meter or trainer?
Lyra. Then be suspicious of any jump that arrives with new kit. A fresh calibration or a new trainer can read differently, and that looks exactly like fitness. Decline it, ride a few sessions on the new device, and test properly. Same goes for a number you know you couldn't hold for anything like an hour.
James. And for anyone racing? Does the critical power side matter more for them?
Lyra. It does, because W prime is what you spend in attacks and on short climbs. WattPlan uses critical power and W prime for the W prime gauge in the player, the live readout of how much of that reserve you've got left. So when it offers new values after a hard interval session, they're worth a careful look before a racing block.
James. Where does this run out?
Lyra. The 0.95 rests on small studies. The MacInnis riders were eight trained men, and the hour came out nearer 90 percent for them. The two parameter model is a simplification of a much messier body. And a single ride is a single ride. Detection is a nudge to look, not a substitute for a test.
James. So what do I actually do this week?
Lyra. Three things. When WattPlan suggests a new FTP, in the player or on Today, check it against your last few sessions before you accept it. If the number came from a race or a group ride, a twenty minute FTP test from the library, ridden after an easy day, settles it. And ride one hard session in the player, VO2max or threshold, so the critical power check has something real to fit.
James. So it only speaks up at three percent, it always asks, it learns from the hard stuff, and my outdoor rides count too. And I'm still the one tapping the button.
Lyra. Which is the point. A detected FTP is a question from the app. Only you know whether you could hold it for an hour, so answer it honestly.
Lyra. The full article and every study we mentioned are on the WattPlan blog, linked in the show notes. And if you've enjoyed this, follow the WattPlan Podcast wherever you're listening, so you don't miss the next one.
James. And if you want a plan built around the time you've actually got, get WattPlan on the App Store or Google Play. Thanks for listening.
Voices produced with ElevenLabs. James's voice is a clone of his own, Lyra is an AI voice, and James reviews every episode.
An out-of-date FTP quietly ruins a training block. Set it too low and every workout is easier than intended, while setting it too high has you failing intervals for weeks and concluding you are going backwards.
WattPlan watches for both your threshold and your anaerobic capacity moving, and the rules behind that explain why it sometimes says nothing after a ride that felt enormous.
How does WattPlan spot a higher FTP?
The classic estimate takes your best twenty-minute power and multiplies it by 0.95, and WattPlan applies the same arithmetic to the best twenty minutes in a ride.
It prompts when the resulting figure is at least three per cent above your current FTP. Below that, the difference sits within the noise of a good day, a cool room or a fresh set of legs, and changing your zones for it would be churn rather than progress.
It will not change your FTP on its own, only show you what it found and ask. It also will not lower your FTP because of one disappointing ride, because a bad day is not a fitness loss.
The curve route to critical power and W′
Separately, after a ride recorded in the app, WattPlan estimates your critical power and W′ from the shape of your power curve, and uses them for the W′bal gauge rather than your FTP. The estimate uses the Monod two-parameter model, fitted by linear regression across durations from one minute to twenty. Critical power is roughly the effort you could hold for a long time, and W′ is the finite amount of work available above it. There is more in W′ and W′bal explained.
For this it merges the current ride with up to ninety days of history, taking your best at each duration, so a single strong ride does not have to carry the whole estimate.
It prompts when critical power has moved by five per cent or W′ by ten per cent, and only when the fit is good enough. The estimate carries a confidence rating derived from how well the regression fits and how many durations contributed, and a low-confidence estimate is discarded rather than shown.
Why does it stay quiet after a sweet spot session?
A critical power estimate needs efforts at genuinely different intensities. A steady session gives you one intensity repeated, and fitting a curve through that produces a confident-looking number that is essentially invented.
So before estimating, WattPlan checks the ride has enough variation to be worth fitting. Your one-minute power has to be at least eight per cent higher than your ten or twenty-minute power, and your best short effort has to exceed 102 per cent of your current FTP, and a ride that fails either test is skipped.
In practice it looks at VO2 max sessions, threshold work, tests and races with attacks in them, while ignoring sweet spot, tempo and endurance rides, which make excellent training and terrible measurement.
Why it asks rather than acts
Changing your FTP changes every power zone and workout in your plan, which is a large change to make on the evidence of a single ride.
Decline the prompt when the ride was unusually short and sharp and the estimate has extrapolated from it, or when your power meter has just been recalibrated or replaced, or when you rode a new trainer for the first time. Decline it too when the number is flattering but you know you could not hold it for an hour, because you will spend the next month failing intervals.
Accept it when the number matches how the last few weeks have felt, when it comes from a real test, or when you have been finishing sessions with something left.
Does it work on rides from Strava, Garmin or Wahoo?
Yes, when the ride arrives with its full power data. Strava, Garmin and Wahoo rides that come with second-by-second power have their power curve worked out on the way in, including your best twenty minutes, and the Today screen reads it from your five most recent rides with twenty minutes of power. A ride that arrives as a summary only, an average with no stream behind it, has no curve and cannot set it off. When one clears the same three per cent bar, Today shows "FTP looks higher" with the ride it came from, and you can accept it or tap Not now, which keeps it quiet for a week and after that asks only for a higher number.
At the end of a structured workout in the app's player, the same check runs before you leave the ride, so Today does not ask about it again. Strava's estimated power, from a ride without a power meter, is never used.
Outdoor rides and races are fair game, which is why the reasons to decline above matter. A flat-out group ride can put a number on the screen that you could not hold for an hour on your own.
If you want a definitive answer rather than a detected one, ride a test. The library has them, they are built so you can exceed the target rather than being held to it, and twenty minutes of honest discomfort resolves the question for the next couple of months.
Sources
- The Reliability of 4-Minute and 20-Minute Time Trials and Their Relationships to Functional Threshold Power in Trained Cyclists, International Journal of Sports Physiology and Performance
- The Work Capacity of a Synergic Muscular Group, Ergonomics