Steep drop in 'Fatigue' for current day before activity

I’ve noticed something recently on the Fatigue/Fitness chart that, to me, looks like it’s not right. For the current date and before I complete any activity the ‘Fatigue’ line drops very precipitately and what looks to be steeper than a couple of days ago when I took a day off.

From yesterday (Tue Aug 18) to today my Fitness has dropped from 100 to 60 (Red arrows). While a couple of days ago it only dropped from 117 to 102 from a day off (Blue arrows). I think I have noticed this similar steep drop off before but never really took note of it.

I assume this is an error and it then affects the future predictions of ‘Fatigue’.


Also, IDK if this changed in the recent past but I would prefer that the current date would use the planned TSS value for the chart until an activity is logged. I typically workout in the afternoon so this means that if I look at the charts during the day then it looks as if I am not going to complete the workout.

The difference in fatigue drop is caused by the difference in workout load from the workouts done 7 days ago. Fatigue follows a 7-day timeline. A couple of days ago, the dropped workout was lower in load then the one that got dropped today.

It’s not like I did a 600TSS ride last week that dropped off the average. It was like 150 or so. I highly doubt that would cause a 40% drop in ATL. I found a calculator online and it gave a ‘Fatigue’ of 87 if today was a zero, which seems more correct to me.

Also ‘Fatigue’ isn’t just a straight 7day average of TSS. There is a 7 day decay factor.

Using TrainingPeak’s equation:

  • ATL = yesterday’s ATL + (today’s TSS - yesterday’s ATL)/7

ATL = 100 + (0-100)/7 = 85.7

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When you are looking at today then any workouts planned no longer count towards fitness and fatigue, only completed activities. Thats probably what you are seeing.

Yeah I understand that. It just didn’t seem right to me that one day of no TSS would drop your ATL from 100 to 60 when several days before a day of no riding only dropped me from 117 to 102. The math just didn’t seem right to me. I could be wrong though it just seemed strange.