Hello everyone
I practice endurance sports since about 10 years.. In the last two years I started to do skimo racing as my main sport and trail running in the summer. I use the UA methodology since a year now in my trainings. During this period I did three HR drift test showing significant improvement. The latest test suggests I that my aeT is close to 172 bpm. That high value raised some questions: 1) Did I got good results on HR drift test? 2) Do I have sort of an anaerobic deficiency? 3) Should I add more intensity work in preparation for the coming skimo season? I hope you will find those data interesting.

For every test, I start with 15 min of easy jog, followed by 5 to 10 min of running drills before starting the test. I always ran for a little more than an hour (66 to 68 min.). My running speed is very consistent through the whole duration. I assume constant speed when calculating HR drift. All tests were performed with temperature between 3 to 12 C and light wind, except the second one where the wind was moderate. I do not use the GPS to track the speed and distance; I calculate it from the lap duration and real lap distance. I use a chess strap HR monitor.

First test December 2019
Place: 405 m track
Time: 1:07
Distance: 15,8 km
Avg pace: 4:15/km
Starting FC (first third avg): 162
Ending FC (last third): 170
Drift: +4,2 %

Mostly nose breathing but starting to be hard in the second half. Slight acceleration in the second half from 1:44 to 1:42 per 405 m laps. Felt god after the test and the next day, I did a 4h run on snow in Z1-Z2 (25 km 1350 m of D+).

Second test April 2020
Place: 1500 m perfectly flat loop
Time: 1:06
Distance: 16,5
Avg pace: 4:00/km
Starting HR: 163
Ending HR: 165
HR Drift: 0,6 %

Increase of pace from 4:15 to 4:00 compare to the first test (5.8 % faster). No clear change in the AeT, but drift is lower so maybe there is an increase.

Felt well during the test, the main limitation was muscular endurance; I am not used to run that fast and on flat terrain for so long. Drop of 40 bpm after ending the test. Some trouble with FC monitor during the beginning of the test. It goes to crazy high values after 3 min in the test and stabilizes after about 12 min. I just ignore that period to calculate the HR drift.

Third test September 2020
Place: 400 m track
Time = 1:08:22
Distance = 18 km
Avg pace 3:47 min/km
Strating FC: 172
Ending FC: 175
HR Drift: 1,74%

Increase of pace from 4:00 to 3:47 m/km compare to the second test (5.4 % faster). AeT have increase from 163 to 172 (+5.5 %) but the last AeT estimate of 163 is probably too low so the increase would also be lower.

I felt good during the test. I was breathing thought the nose for the first 12 min. to set in the pace. After this, it would not really have been comfortable to only breathe through the nose. Again the main limitation is muscular endurance; I am still not used to run that fast and on flat terrain. I could have maintained that pace for at least 10 more minutes. Felt well the next day, but my calves were sore. HR monitor still have some problem in the first 10 minutes of the test, so I rejected some data.

AnT estimates
I use skimo races as estimates for AnT, even if those events are usually longer that an hour. In the first ascent I basically push like if it was the last so I should be close to AnT. I pick the highest HR value as my AnT.
January, Stoneham Skimo race duration 1:17 ant=171
February, Burke Skimo race duration of 1:47 ant=174
February, Orford Skimo race duration of 1:01 ant=170
March, Mont Sainte-Anne Skimo race duration of 2:04 ant=174
July, Uphill run duration 25 min. ant=178 (178 is the max FC, but avg is 173)
September, Mt Rundle ascent duration of 1:25, ant=175 (HR is dropping at the end because of rough route and snow on the ground; Felt great the next day and climbed Mt Temple by the scrambling route)

During 30-30 (2X 12 to 14 rep.) uphill running trainings, 183-185 bpm feels like the max I can go, so my AnT is below 183 bpm.

What I did for training in the last year
I consistently did 6 to 14 hours of Z1 –Z2 training, some weeks I reached 20 hours. Most of it is done on skis in the winter (70 %, the rest is running) and in the summer I run/hike (80 % on trails or off trails and 20 % on flat roads).

Most of the week I do one intensity training, Most of it is in Z4 (30-30 uphill). I rarely do Z3 intervals, the time I spent in it is during races or long run/ski activities. On average I spend about 5 % of my training time in Z3 + Z4. The peak weeks are at 10 %.

I did a 12 week gym ME progression last spring and did a couple of maintaining trainings during the summer.

Discussion
Is it possible I got bad results/interpretation from the third HR drift test? 173 bpm seem to be very high, could it be above my AnT, explaining why it plateaus. On the other hand, the pace progression seems to fit with the first and second test and the HR drift is low. I also still had some reserve to go faster or longer so I should not have been at AnT, thus I assume that there was space for HR drift during the test. I would consider the 172 bpm value good and used 170 bpm as AeT on the field. The low drift of 1,7 % of HR drift could suggest AeT higher, but I don’t think it is really the case.
Assuming an AeT at 172 bpm and an AnT close to 175 bpm, my Z3 is basically absent. Moreover, I really struggle to get to 183 -185 bpm, therefore I only have about 10-12 pbm between AeT and something like max HR. Does it mean I have sort of an anaerobic deficiency? I guess I should add more intensity work in my training plans. I think I will try to do longer Z4 running intervals (2 to 3 min.), every 5 days, any other suggestions?

I guess It could also be interesting to test AnT on flat terrain, I may try a 10 km test this fall and post results here.

I find those data interesting regarding the significant speed improvement on flat terrain, even though I have not work on that specific ability in the last year. The gym ME could have an effect even for running on flat terrain.

Thanks for reading