I’m not sure you failed the test. If you grab the final hour and count everything before as a warmup, you get an average of 140 for the first half, 145 for the second. The difference of 5 bpm makes the drift come out to 3.4%, which is just below the 3.5% threshold. Grabbing the first five minutes of that hour puts your AeT at 135.
I take the average of the first five minutes because a coach here once suggested that, and it seems to make more sense to me than trying to stabilize your HR at the exact bpm you think it might be.
You could maybe bump it to 136 because you were below the threshold, but this is a pretty good test from what I can see. I see the spike, but I think that once you got into the test, your heart rate stabilized at a higher rate than you realized it would. The drift is what you’re measuring, and your hr was drifting right within range.
First half – 140 bpm
Second half – 145 bpm
Drift – 3.4%
First five minute average – 135