As I dont like explicitly going for breakthroughs very much, I am with No Decay since last autumn, and having had my last breakthrough in April 2020, my signatures are adjusting according to my weekly training load, which ranges from 100 to 115. At the moment, I am doing a mixture between Xert workouts, group rides on Zwift and free rides, having set my phase to Post Event since I have no specific targets this season. Anyway, as a result, I expected my TP to be somehow "diluted", but having done a 65 km group ride on Zwift this week, which unintentionally turned into a sort of a mini race, I got a Near Breakthrough for the last effort until the finish line. Surprisingly, my TP only declined for 2 Watts (HIE declined for 1.5 kj, PP didnt change), which brings me to the conclusion that the No Decay Setting can be a reliable predictor for the Fitness Signatures over time, especially when doing a great amount of riding. Do you think I am right?
I found otherwise, but from very different rides. Started pre-base 1st Jan from untrained, and did mostly turbo endurance sessions 60-90 mins, with the odd sweet spot up the Alpe du Zwift. From a baseline of maybe 190W TP it had me up to 245W TP by the end of Feb, and LTP at 210W. Trying to sustain 210W up the Alpe for 80 minutes was an absolute killer, no way was that LTP.
I changed to Normal Decay (as I’d been on all last year) and flagged a ride last year to trigger a recalculation and it dropped my TP to 215 and LTP to 175 which was way closer to expectation.
For whatever reason, No Decay was vastly over-projecting my capabilities.
No Decay’s effectiveness is dependent on the quality and completeness of your entire dataset. If you have invalid gaps or if your breakthroughs aren’t accurate or are infrequent, it can make it much harder to extra/interpolate your fitness accurately.