First of all, I have already reported this issue in detail on r/Garmin, but I believe it is necessary to raise it here as well, since the problem has persisted for years now, unless I have completely misunderstood how Garmin's calculations work.
No matter which Garmin device I use, my High Aerobic load is permanently stuck at zero. This is not a new issue. It happens cyclically and repeatedly for several months every year. Since I've read hundreds of similar discussions over the years and none of them has ever solved my problem, let me clarify a few things upfront:
Yes, my High Aerobic load is exactly ZERO
Yes, my heart rate zones are set correctly
Yes, I train for hours in heart rate zones 4 and 5
Yes, I also use a power meter (for whatever it’s worth) with properly configured power zones
Yes, my weight, FTP, personal data, and everything else are correctly entered
I see only two possible explanations: either this is a bug, or Garmin's calculations heavily penalize athletes who practice long-duration endurance sports. Let me explain with two examples.
connect.garmin.com/.../21937045842
In this activity I performed 8 high-intensity intervals, totaling 10 minutes in HR zone 5, 50 minutes in HR zone 4, and 1 hour and 23 minutes in HR zone 3. Despite this, Garmin labels the activity as Base (Low Aerobic), simply because after these very demanding efforts the rest of the ride was easier. The final result: High Aerobic Shortage, literally zero.
connect.garmin.com/.../22023520213
Here I spent 1 hour and 10 minutes in HR zone 4 and 1 hour and 30 minutes in HR zone 3, yet once again Garmin classifies the activity as Base (Low Aerobic), for the same reason: the remaining part of the ride was easier. Once again, the final result is High Aerobic Shortage, zero.
I may not be an expert, but I've always found Garmin's evaluations in these cases to be highly inaccurate. I could do 1 hour in HR zone 5 and end up in the hospital, but if I then ride 2 hours in HR zone 2, Garmin would still consider the workout "Base", basically a walk in the park. How does that make any sense?
In many endurance sports, a workout typically includes a relatively short portion of very demanding intervals, followed by a much longer period at low intensity. How can this type of training be classified as purely Base?
In practice, the only way to see anything other than Base as the Primary Benefit is to do short workouts: 10 minutes of warm-up, 30-40 minutes of hard intervals and 5 minutes of cooldown. In that case, the Primary Benefit will show VO2 Max.
But if instead of a 5-minute cooldown you decide to ride for 3 hours in HR zones 2 and 3, Garmin doesn't "reward" you, it completely dilutes your Primary Benefit, which inevitably becomes Base. And that's where High Aerobic Shortage probably comes from.
In short, I strongly suspect that Garmin penalizes athletes who combine high-quality intensity work with high training volume. Do you think this part should be reworked?
