[Dimitri]

I agree with you; the steepness of the slope is part of the explanation. But even more relevant is the fact that I “clogged” myself. This is what my coach told me, and it makes perfect sense. Here is a very interesting article written by Scott Semple that explains the phenomenon:

Clogging Up the Drain: Why You Are Forced to Slow Down

In summary, I went too hard at the very beginning of the test (too hard, meaning even higher than my AnT), and therefore, I was producing more lactate than my body could eliminate. When this happens, the body forces you to slow down in order to use the lactate shuttle to eliminate the lactate excess. The rest of the phenomenon is explained in the article: “To speed the clearing process, extremely slow speeds are required. So, in a race context, if you start too fast, your average speed for the event will be much slower. If you start without the burst, you avoid the initial flood of lactate and the slow reabsorption period.” This is exactly what happened. My system was overflowed by metabolic byproducts (mainly lactate). Consequently, I was forced to slow down at a much lighter pace than my AeT.

It is funny to witness how this phenomenon destroys performance. During my last AeT test, I was able to climb 1260 meters of elevation gain in one hour. During this failed AnT test, I “only” climbed 1080 meters of elevation gain in one hour. And, of course, when you run at AnT, you’re supposed to perform better than when you run at AeT.