I did a big day yesterday with an XSS of 249. With the freshness slider set to 0 XERT tells me that today I am fresh and should do an Endurance activity of XSS 145. I know I can alter my freshness using the slider and flip between XSS 145 or a recovery ride but what I want to understand is how XERT can determine I am fresh the day after such a big XSS day?
Your status is based on a exponentially weighted moving average. If you have a strong base built (relatively high Low Training Load) and your ride is made up of mostly low intensity, the conditions that defined “fresh” return fairly quickly due to the time constants. You’ll likely enter “tired” status quickly if you were to do another ride but according to the numbers, you won’t need a lot of rest time before your status returns to “fresh”.
The ride was 1 hours 45 mins of Tempo, 30 mins of Threshold, 9 mins of Vo2 Max, 35 Mins Endurance and 13 mins of recovery, intensity factor of 82% … I’m not sure if that qualifies as a low intensity ride, my perception was that it was not but it is longer than my normal rides so I may be confusing duration with intensity. I was looking forward to a guilt free day off today but I had to make do with a guilty one instead 
Thanks Steve. That’s really good feedback for us. We always say to pay attention to how you feel first and foremost and to use the Freshness Feedback to affect how the system is determining your freshness level. Having said that, we are always happy to get feedback on when there are conditions where the current math calculations could be adjusted to account for possible greater affects both in terms of actual improvement or from additional acute fatigue. Shouldn’t feel guilty where you are legitimately feeling tired.