How to Tell It’s Time to Update Cycling Power Zones

By Chris Carmichael,
Founder and Head Coach of CTS

Power meters are everywhere, and now with app-connected smart trainers and smart bikes athletes indoors and outside are training with power. All that data is great, and advanced training software can help make sense of it, but as a coach I see athletes making two big mistakes: not uploading their data consistently and not adjusting their threshold values and cycling power zones to reflect improvements or declines in their physiology.

Inconsistent Uploads

The more complete record of your efforts, the more accurate picture you’ll get about the true state of your fitness. If you are training well, but there are holes in your data, charts like Strava’s ‘Fitness and Freshness’ and TrainingPeaks’ ‘Performance Management Chart’ (PMC) will understate your true training load. This can be harmful if you are using the training software to gauge how much fatigue you are accumulating, because not all of your training stress will be accounted for. Consistent data provides a fuller picture of your training history, allowing you to discern patterns and see why you had great or poor performances during a certain period.

Failure to change FTP value when you improve

The Functional Threshold Power (FTP) or threshold value you use to establish your cycling power zones should not be a ‘set it and forget it’ number. When your training is effective, your sustainable power at lactate threshold will increase. Many athletes recognize they are getting stronger but fail to update their training ranges. In some cases, this is because they know updating ranges will make interval workouts harder. It’s nice to feel strong, hit your ranges consistently, and bang out perfect intervals. In the big picture, there are fewer risks – and many of the same benefits – from setting ranges a little low, but eventually you have to increase them to keep making progress

When your threshold value is set too low, it skews the calculation of your Training Stress Score (or Relative Effort in Strava). These scores are calculated by comparing your current performance (normalized power) relative to your FTP. If the FTP value is lower than it should be, the training software will overstate the time you spent above threshold, which raises the stress score for that workout. For athletes who like to watch the blue Chronic Training Load (CTL) line on the PMC go up and up, CTL looks at the previous 42 days of your training. If the stress from individual workouts is being overstated, then your CTL, which many athletes consider to be their fitness level, will also be skewed to look higher than it actually is.

Failure to change FTP value when you lose fitness

It is equally important to reduce your FTP value when you lose fitness. Athletes are often reticent to notch this value down because it is a blow to their pride, but using accurate values to guide your training will help you raise those numbers again. And be patient. Many athletes want to rush to increase the value back to where it was. Remember, a little low is better than too high.

What happens if your FTP value is erroneously elevated compared to reality? Even when you are working hard, the training software will understate the training stress from your rides. This can be disheartening because the software isn’t going to reflect the progress you are actually making. It thinks you’re riding at an aerobic endurance pace when you are actually riding at your current lactate threshold power. In the worst-case scenario, keeping your FTP set too high can lead to an overtraining scenario. The software makes you think you are training at a lower stress level because your current power outputs are low compared to your old FTP. That encourages you to ride harder or pile on more miles and hours than you are currently prepared to handle.

When to Change Your FTP Value

CTS Coaches use TrainingPeaks to prescribe training, but no matter which software you use, there’s probably a notification that gets sent out when you “set a new FTP”. It’s a reminder to update the value that software uses to establish cycling power zones and calculate training stress, based on a recent performance. I appreciate the heads up of a 5-watt improvement, but I think you should think of those notifications as kudos rather than requirements. A particularly great day on the bike can be just that–one great day. And even that performance that looks like a 15-Watt bump in your FTP could have been influenced by a few days’ rest, a good night’s sleep, an accomplishment at work that fired you up, or the added motivation to stay on your buddy’s wheel. Performance is not always physiology.

Similarly, when athletes take some time away from training, either on purpose or because of injury or illness, their fitness diminishes. The return to training is almost always gradual, rather than jumping straight into field testing or hard events to determine a new FTP value. I recommend riding by perceived exertion for two weeks before adjusting any power ranges.

I recommend updating training ranges once you have three data points that indicate your power at threshold has changed, either up or down. Ideally, at least one of those data points should be a field test and the other two can be hard solo rides, group rides, or races. Today’s training software programs are extremely powerful tools, but they only work as well as the data you put into them.

TrainingPeaks®, Training Stress Score® and Normalized Power® are registered trademarks of Peaksware, LLC.