I don’t pretend to have all the answers but I might be able to help you understand these results a little better and how they might be used in your training.
The first thing I can say is that you are a slow twitch athlete (ST dominate muscle fiber type). I know this because your blood lactate levels were so low for all of the test but especially in the beginning. This might be due to genetics or your training history of lots of endurance training. Either way this is good news for you considering that kinds of activities you like.
You probably recover quite well from big days in the mountains. You are also probably will not be trying out for the high jump team or the basketball team 😉 By this I mean you probably do not have a great vertical jump height 🙂
Just because you could do a long mountain run like in October and have an average HR of 156 does not mean that is your aerobic threshold. It is possible to have an average HR in Z3 for mountain runs because of the change in gradient of the trail. I doubt you could run on flat ground for the same time these runs took you (2-4 hours maybe) with an average HR of 156.
With athletes like you with very low lactate levels it is not easy to get the AeT from a lactate test. It seems that they have chosen the HR at which lactate levels begin to rise. I can understand that reasoning but I suspect it is too high. The fact that this was well above a conversational pace also indicates what I mentioned above. I doubt you would consider this pace was not sustainable for 1,2 or 3 hours.
As a comparison to this lab test I suggest you do a HR Drift test on a treadmill and see if you also get 157. I suspect you will not and that the AeT HR from the drift test of a conversational pace will be closer to 145-150.
Next I suggest you conduct a field anaerobic threshold test. I much prefer them to either a lactate test or a gas exchange test. Both those tests (gas exchange and lactate) are looking at proxies to help establish this number. Both these tests are steps tests with only 3 minutes spent at each speed. You are transitioning through the intensities.
Where as a field test is an actual performance test. You will run up hill as hard as can (after a good warm up) for 45min. The average HR during that test IS, by definition, your AnT HR. That is the maximum HR or speed or vertical rate of climb or power that you can sustain for many minutes. The normal duration is 30-60min. Thirty min for the less fit and 60 min for the elites. For you 45 minutes.
See what these two tests tell you and report back.
I hope this helps