I don't fully understand the Decay options

Hey Guys
I need some help , i’m doing a Centry Rider , Moderate Improvement Rate plan .
Problem is i’m not sure what Decay i should be on ?
as experiment i flicked through all the options to see how the assessments of my TP changed and they were massive .
No Decay : 272 , Small Decay: 263 , Optimal: 239 , Aggressive : 207 !!! Original : 272 .
I’ve been using No Decay for months and i’m sort of stuck , Help , what am i doing wrong.
Thanx in adavnce

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Optimal unless you plan to do nothing but base training and have been doing that instead of a variety of workouts including BT efforts.

Short take: http://baronbiosys.com/glossary/signature-decay-method/

Long take: http://baronbiosys.com/xerts-magic-setting/

Thanks for the reply
If i put in Optimal it will reduce my TP to 239 which is far far to easy .

Then recalculate your signature by using the power curve calculator page. This assumes you know the correct input values for something like 1 sec, 5 minutes and 20 or 30 minutes.

I think 273 ish is pretty accurate , i just don’t understand how it came up with 239 or 207 which is way out .

If you start experimenting, read the literature and understand what each option means and why/when it should be used.

Furthermore, if you use each option and nuke the system by doing a total recalculation, this is what may happen.

If you think 270-ish is fine, use that as 60 (3600 sec) in the calculator together with other values you know, after you have set the decay to optimal.

Just work from there and do not do a complete recalculation.


Altough I cannot explain why this is caused you still could try, after setting it to “Optimal”, to force a breaktrough to get the TP to a more realistic level. That way I think you have the most accurate TP back again.


Once we figured out we could extract a signature from an activity with a maximal effort, we needed a way that we could dynamically track that signature on a day to day basis. We didn’t want to do something crude like FTP testing, where your numbers stay exactly the same until 4-6 weeks later when you test again (or when you get another BT). Instead, we decided to track the signature by implementing signature decay. Its very helpful in a dynamic environment like Xert, where workouts and rides aren’t uploaded every day. They leverage the time constants for each parameter (low, high, peak) in order to determine how your signature responds to training (XSS) and recovery (how the signature decreases when you dont train).

No Decay looks at your historical TP, HIE, and PP alongside their respective training loads (Low, High, Peak) and makes assumptions about what your TP, HIE, and PP are based on the historical relationship between the two. IOW, if you generally always had a TP near 270 W with a LOW training load of 75 and you get your current TL to approximately 75, the assumption is that your TP is likely somewhere near 270W. Because it’s based on training loads that are constantly bumping up with training and decaying over time, this setting will result in the most fluid/dynamic fitness signatures day to day (but usually nothing that would make a substantial difference during a workout - +/- 1 W TP, 0.1 kJ HIE, 5 W PP, etc). This can be good when doing a long base phase, but should be used with caution… if the signature ever becomes too high, there is no decay to bring it to the proper level. This is why we generally recommend switching back off this mode when you’re pushing for breakthroughs semi-regularly.

Optimal decay essentially prevents your signature from rising or decaying if you’re steadily increasing your training load. This results in an XPMC that looks sort of like a staircase - signature jumps up during a BT and then stays level until the next (when TL is increasing). If training levels drop, the signature will decay at the same rate as your training loads. This is generally the best mode during the build/peak/taper/post event phases (or if you’re riding for general fitness). You still need to push to get BT’s that increase your signature, but the signature wont continue to decay lower and lower if it’s been a few weeks/months since your last BT.

Small/Original/Aggressive all let your signature decay every day (at different rates, with small being the least decay/day and aggressive being the largest decay/day), regardless of your training. This is best if you’re worried about your signature being overestimated, or if you perform a lot of maximal efforts in your weekly training.


Thanks to everyone for your help , i’m pretty certain i’ve got it sorted now , sadly the best way to learn is screw it all up as it’s forced me to ask questions and read through the litreture .
Love the software
Regards Wayne

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