Why Is Functional Threshold Power (FTP) So Important to Cyclists?
If you have spent any time cycling for more than just casual fitness, you will know that power output is the measure of riders. Putting watts into the pedals is how you get moving. The only other considerations are how much weight you have to move (either in your body or on a bike), and how aerodynamic you are.
Since bike weight and aerodynamics are irrelevant for stationary cycling, functional threshold power (FTP) is often talked about. There are two reported numbers for FTP. The first is an absolute number which notes the average wattage output. The second value is a watts per kilogram measure, which takes into consideration the weight of a rider. This weight based metric helps to normalize between riders that are vastly different sizes.
I personally know fairly out of shape 260 pound+ riders who can throw down watts that make them appear on par with some elite cyclists. Get them on even a moderate hill though and powering that weight up next to a 130 pound rider next to them is gonna expose the differences.
Peloton instructors highlight that weight will make a difference, and most of them avoid speaking directly about specific FTP or power zone values (although they slip in at times). Peloton FTP reports only an absolute value and doesn’t specifically consider riser weight. Coupled with the fact that different bikes will be uniquely calibrated, the fact of the matter is that you will have a hard time comparing your cycling performance to another rider if all you have to go on is their one time FTP score.
How do Strava and Peloton Estimate FTP?
Both Strava and Peloton use a 20 minute average to calculate FTP. From Peloton FTP calculations “First, subtract 5% from your FTP Test average output number. This result will be an accurate estimate of the average output you could hold for 60-minutes (i.e. your FTP).” and for Strava “the easiest way to calculate your FTP is to test your best average power for 20-minutes and then subtract 5%.”
Although the definition seems the same, Strava produces an on-going estimate even from longer rides. Peloton on the other hand updates FTP manually unless you do an FTP test. That means that if you do a 60 minute ride, and wind up well above your previous FTP score Peloton will not automatically update. Strava will wind up clipping the output curve of the longer effort and providing that number as the estimate FTP.
Will Peloton Automatically Update My FTP?
Peloton will automatically update your FTP ONLY for completed rides of a designated FTP test. This means that if you do a better effort on a non-FTP test 20 minute ride, or you manage to produce a larger output on a 20 minute section of a longer ride that Peloton will not automatically update.
If you simply do not perform will in FTP tests, or if you have gotten fitter since your last one and want to use a new value to calculate Power Zones, then you will need to manually update. Other than calculating Power Zones, there is not much benefit to keeping your FTP updated. Even if you do have a higher FTP, there might also not be a need to recalculate Power Zones.
The above images are from an actual FTP test on Peloton, then a 30 minute ride a few weeks later. The 30 minute ride averaged to 307 watts, while the individual power curve for it had a 20 minute reading of 314. On Strava the estimated FTP equals exactly this 314. Both of these rides were done on a Peloton, so the difference in calibration of a power meter should be irrelevant.
Although this might seem like a huge difference from the 263 watts FTP produced on the test the real impact to power zones is not all that drastic. When doing Power Zone classes it is easy enough to just stay at the higher or lower end of a particular zone, rather than dealing with the hassle of keeping the settings up to date.
Are FTP Estimates Accurate?
In short, FTP estimates *may* be accurate, but it is somewhat irrelevant. More important is there consistency and precision. It is important to consider that FTP and power output will be dependent on the calibration of the power meter. Peloton has this integrated but stories across the internet suggest that bike to bike variations will produce wide ranges in power output, and subsequently FTP. Similar things go for different power meters on a road bike or trainer
For both Strava and Peloton, if you wish to manually update your FTP it can be done within the settings of the app or bike. So if you are going to set and updated a FTP manually make sure that there is some indication that the setup of where you produced the FTP test match that of where you will be riding regularly.
At the end of the day FTP is functional for a few things. The first is to produce a nice linear line on power charts, for that the accuracy of an FTP is irrelevant as you could simple draw any horizontal line. The second reason is to control training in different zones. Again here the accuracy is somewhat irrelevant, although the precision is important.
If you measure an FTP on a Peloton of 500 watts, you may be an elite athlete or need a calibration of your bike. So long as you wind up riding on the same bike though, the calibration does not matter. Peloton does not currently have any real rewards for leaderboards so there is no reason to overly concern yourself if your FTP seems wrong compared to friends.
Resources for Learning about FTP?
FTP is a specific time measure, but cycling is about how much power you can output over various times. All else being equal (rider weight, aerodynamics, bike efficiency) if you put more power into your pedals than the rider next to you, it’ll result in going faster. Of course it is nearly impossible to make the other influences equal, but even so power output is a crucial predictor of speed. This article discusses what a good average cycling wattage is.
How to Update FTP on Peloton or Strava
Whether you took a test on a different device or just want to manually update your FTP based on a change of fitness, changing your FTP will alter your anticipated power zones.
On Strava you can update FTP using the web (not app). Navigate to Setting>My Performance and you will see FTP. Put in a new one, and a date. Keeping historical FTP ensures that pace zones of an activity match your recorded FTP at the time.