Zero Anaerobic Effect After Hard Run

How does Garmin calculate Anaerobic effect exactly? I have been using my Fenix 5 for a good few months now, so it?s dialling in to my training nicely now. It?s got to the point that I am starting to really rely on the data it provides me. I have also started to use the HRM run too and that is starting to give me more good data. Yesterday, however, I did a hard run in atrocious weather where I was in my maximum HR zone for a good 3 Miles. When I finished my run I got an Anaerobic effort of zero.

Does anybody know what this may be the case. As I said my HR was in max for a good 20 mins.
i did lose GPS for a short period which gave me bad data but I wouldn?t have thought Anaerobic data would require GPS data to calculate.
  • I'm guessing the treadmill may be part of the issue. 

    How was the watch measuring pace during your treadmill workout? Did you use the pace estimated by the watch, by a chest strap like the HRM Pro, or a foot pod?

    New anaerobic recommendation is  7 x1min @ 8:10/mi. 

    That seems like a good structure. 

    Ignore the speed recommendation and do a maximal but steady effort. Don't hesitate to walk instead of jogging during intervals. You will get a poor execution score, but the anaerobic effect will be better measured if there is a strong contrast between the high effort intervals and the rest periods.

    Finally, since your target for anaerobic workouts is too low, you should check your HR Max and do a new LT running test runnning outside with GPS or a foot pod.

  • watch underestimated a little.  I think the watch underestimates my anaerobic level, since it is giving me the speed.  I am better at shorter distances.  Overall, I think I have a handle on it.  I will ignore the speed recommendation, and run at the higher pace, even if I think it will be hard(read impossible) to maintain.  Currently training for first half in the spring and full marathon in the fall.  Speed workouts aren't as important as getting the miles under my belt.  I do notice the race predicter seems to jump when when I get a decent anaerobic workout in. wish me luck.

    Edit: Winter sux in the north east, I am barely able to to run outside once a month now.  I really think it is confusing the watch(965) since most of my runs are on the treadmill.  VO2 max, and the race predicter jumps when i run outdoors.  I am looking forward to running on the track for the sprints.  I last ran on the track 35+ years ago.  Running a marathon was a bucket list item from way back when.  Sad, but getting my watch 3 months ago got me off my @$$ to go for it.