Re: Ant test
Maybe you didn’t go hard enough? Maybe you didn’t ramp-up completely before acquiring the data? I say this because I find the AnT somewhat subjective–ie it depends on what effort you decide (unconsciously or consciously) to put into it. And of course it also depends on other factors like, sleep, fatigue, diet, and heat. Also, your AnT seems to have been 175 in the past but its now 168? I presume you just ran as hard as possible for 30min after ramping up for say 15-20min? As you may know, during this test you don’t pace yourself or follow your HR–you just go all out and then check the average HR for the later portion of the test period (or the average pace if you want AnT pace). I don’t think there is much use in checking drift for an AnT test, I presume if one did it would often be present, and may simply indicate that one started collecting data prior to achieving ~lactate steady state (AnT)–ie, a portion of the data set was contaminated by effort above or below AnT.
Re: AeT Test
If you had <5% HR drift at 160, then I would try a test at 165, etc. The nice thing about the AeT test is that it can be easily performed multiple times per week since many of us do Z1/Z2 runs multiple times per week anyway. Another way to look at it is to simply run at 165 until your heart rate reliably rises 7-8 beats (5%) higher than when you started (after the warm-up) and then either slow down at that point or stop–with time you’ll be able to run longer and longer before your HR rises 7-8 beats, and eventually it won’t. Then you can try a higher HR. Alternatively, if you can’t run the time/distance you want at 165 without the HR rising 7-8 beats, then try a lower heart rate next time. I would just experiment with it a bit and have fun. Another way to do it is to just look at 75% of maxHR and call this your AeT and then adjust up or down as described above, or with an AeT test.