Is the stamina feature actually useful?

Even after months, for long rides/runs, its down to 1% after around 50-60 percent. Not useful for me. (Referring to my Epix2 that I own since the beginning of the year and "knows" me because wearing it 24/7.)

I think the feature could be potentially useful. I'm not ready to say that the feature is precise. In my case, the last ride I did was quite bad, I started to feel tired and hungry 30km far from home, and stamina was showing 50%, which was definitely far from how I felt.

The feature is very dependent on the accuracy of your power duration curve. Especially for the shorter duration values as these are the values that affect how it drains when above threshold. 

That makes sense. I'm wondering if Stamina is able to tell part when I'm pacing myself but feeling good and when I feel like crap and I'm bonking. In both cases, power and heart rate are low.

Not sure on that, but it could possible use the performance condition value. All the these values are coming from the Firstbeat libraries 

I like the data page more than anything. Personally the stamina data is decent for pacing longer efforts and can see if the miles left drop a lot on sustained climbs where I can decide to dial it back. Overall though it is fun to look at just not very practical.  

I’ve been actually surprised how close the mark it is. I think as I already had a lot of long term reliable heart rate and power meter data to start with it was good for me from the start.  When I’ve zeroed it mid ride after a max all out climb it does feel like I’m on the limit.  My recovery is fairly good though and if I go steady after a climb it comes back and I do feel ready to go again.  This week after a lot of rides it was showing pretty low - and towards the end of the ride sure enough I was not ready for any hard efforts.  Just rolling along to get home.  

I guess to sum up I’m not “slave” to what it says but I’m quite surprised when I look at the screen and it seems a pretty good indicator of how I actually feel.

This does make sense but my power curve has been very similar for at least the past 3-4 years. I ride EVERY ride with a power meter and external HR monitor. Unless the 1040 didn’t pick up the power curve for all my riding prior to when I got it? That could definitely explain the lack of accuracy, although I raced with it the week prior in a very similar race, although potential stamina seemed to stay positive until end of the race per graphic below. 

It tracks how I feel pretty closely.  What I haven’t really worked out yet is what I do with that information

I think it *could* be helpful for a race tbh but based on what I’ve seen I really cant use it. In races we often talk about “burning matches” it would be awesome if the stamina feature could give you some idea of how many matches you have and how you’ve used them, which may actually change your race strategy during the race.