Xert’s Magic Setting – Signature Decay

Xert was first to introduce the idea that you can obtain fitness information from regular activity data.  We then introduced the idea that your Threshold Power could be calculated in real time, on-the-fly, as you ride.   But in the past couple of months or so, a new feature was quietly released without much fanfare or news.  Some of the users on the Facebook Xert Users Group got a bit of glimpse of it.  Although perhaps innocuous, it actually engages a number of very powerful computational capabilities that bring a lot of what Xert does together into one simple setting: Signature Decay Method.

Why is it a “Magic” Setting?

We’ve called this a magic setting because there is a lot that is going on under the covers, doing things with your data that has never been done before.  For the very first time, software is tracking your day-to-day changes in fitness across three dimensions – low, high and peak energy systems – based on the training and activities you do.  This means that Xert is tracking your day-to-day changes in your Threshold Power, High Intensity Energy and Peak Power.

Imagine that you now have an ability to know much your Threshold Power increased after every single workout, after a group ride or how much you lost after a few days off.

A key aspect of this feature is that you no longer have to do any form of testing whatsoever or even generating maximal efforts for breakthroughs with the Xert software.  Simply ride and train and see how much you are improving day-to-day.

What does Signature Decay Method mean?

By default, signature parameters decay according to a preset algorithm used by the system.  This is what Original means:

You can find this new setting under the Account Settings/Profile tab.  Everyone’s account is set to Original by default.  Do not change this unless you finish reading this blog and understand it!  What this setting means is that once you get a breakthrough, your signature will slowly decay day-to-day.  Over time, each of your three signature parameters will decline.  Why do they decay? They decay because if they didn’t and your fitness declined, your parameters would be overestimated and you’d think you were much stronger than you are.  Workout interval targets would be too hard.  But what if I’ve been training and my fitness has improved?  Under the original decay method, as with many other training systems, you need to test yourself to get your current fitness numbers.  For other systems, this means doing regular FTP tests.  For Xert users, it means getting a breakthrough during your activity.  Many users simply add in an effort here and there, or plan to do a local hard group ride or online race where they intentionally push past MPA and have the system recalculate their signature.  For the vast majority of users, this is the recommended approach.

But what if my training intentionally avoids doing any hard efforts?

If you’ve had long periods where you didn’t push yourself to your limit for a breakthrough then using the current setting, you’ll see a divergence between your Training Load and Threshold Power:

This is the tell-tale sign that your signature parameters are likely underestimated.  One way to deal with this, is to plan (and to regularly plan) for fitness breakthrough efforts in your regular training schedule.  However, if this isn’t possible or to correct a long period of divergence, we now have a solution: New – No Decay.

What is New – No Decay?

When you change the Signature Decay Method to New – No Decay, the system does a number of calculations to help you better manage your signature during times where you haven’t done or don’t plan to do any breakthrough efforts.  (In control systems theory, we would say that the system is going through a period of dead reckoning).

Under the covers, Xert establishes the relationship between your training loads and your fitness signature parameters.  When you have robust historical data, without large gaps without power data and without power meter errors / changes, Xert matches your historical breakthroughs with individual training loads:

In doing so, it is able to perform a bit of magic for you: it can determine what your fitness signatures parameters are expected to be without the need to do any testing or breakthrough efforts whatsoever.

How and when should I enable it?

This new setting should be enabled if, and only if:

  1. You have good, robust historical data.
  2. You are in the middle of an extended period or expecting to go through an extended period where you do not anticipate doing any testing or have any breakthrough efforts in your activities.

To properly enable this setting:

  1. Identify your last good breakthrough activity:  Go back through your history and find the most recent activity whose signature accurately reflects your signature at that time.  Ideally, it should be within that last few weeks or months.
  2. Ensure you have good and complete power data after that point.
  3. Unlock any signatures that have been manually set against activities after the identified breakthrough activity.
  4. Enter in all activities with missing XSS for your entire history if possible.  The more gaps you fill, the better the results.
  5. Change your Signature Decay Method from Original to New – No Decay.
  6. Delete the activity with the identified breakthrough and add/sync it back in to force a trickle-down process from that activity forward.

Once this is done, your progression data will be updated from that date forward:

Notice how in the above chart, Threshold Power declines and increases with Training Load.

When should I set Signature Decay Method back to Original?

Although New – No Decay is a great feature and one that you would think should be on all the time, it should only be used sparingly.  The reason for wanting it off is because you want to prove what your signature is and not have the system predict what it is.  You may be having other health issues, for example, that prevent you from attaining what you had been able to achieve historically.  If you leave this setting on, you may miss the declines in fitness that you are having since the system will not decay your signature. New – No Decay means that the system pegs your signature parameters with your Training Loads and there won’t be a relative decay in values.  If you have errors in your data that overestimates your XSS scores for example, your parameters may not be achievable and may never be until you change back to Original again.

Set it back to Original the moment when you know you’ll be back to performing breakthrough activities again.  This ensures that you keep all the math and algorithms honest with real expressions of your fitness rather than rely on historical relationships to predict your fitness.  Besides, you’ll get more breakthroughs too!  It always feels great to confirm and see your fitness improvements.