Incorrect stamina calculation

From www.dcrainmaker.com/.../amp

“When your Stamina and Potential Staminaare both zeroing out together, expect your ability to race in a meaningful way to be severely compromised.  It doesn’t mean that you are unable to put one foot in front of the other, falling off your bike, or passed out on the ground.

And similarly: If your Stamina is zeroing and you have Potential Stamina remaining, expect your ability to sprint/climb hard to be severely compromised, but you can probably drop your intensity safely below your anaerobic threshold and keep going.”

Stamina factors in a lot of different things, and can vary a lot from day to day. For example, it factors in your sleep quality the night before, and your "body battery", among other things. So if you begin a hike with relatively poor rest, low energy, and/or high stress, your stamina will deplete much faster than usual.

For example, I ran two different 5K runs this last week, both of which were done at a similar pace. On the first run, I was not very well rested and started the run with like 30% body battery. At the end of the 5K, I only had about 30% stamina remaining, and honestly that's exactly what it felt like too - I was exhausted at the end. On the second run, I was much better rested and overall felt a lot better, and had about 70% stamina remaining at the end, and again that was a pretty good reflection of how I felt at the end, I felt like I could've easily kept going if I wanted.

I wonder the same.

Today ( after a few weeks running in only Z2) Garmin Stamina believed i was only able to perform 10 minutes in Z1. - and I ran additional 10 min in Z2, increasing slowly to Z5. A total of 1 hour hard training all the time Garmin explained to me that I only had 10-6 minutes left.