Bill: Doing all Zone 2 might be too hard for some individuals, while doing all Zone 1 might not provide enough stimulus. Putting total sub-AeT training volume in that context, doing everything at the top of these two zones may be too hard for some individuals, affecting their capacity to recovery. If our recovery isn’t optimal, we aren’t optimizing our training.
You can train at the top of the zones it if it’s working over a longer period. If it feels too hard and you aren’t recovering, titrate your intensity (do more in the middle of the zones) so you can recover adequately.
Your assumptions are probably all correct, but the relative importance of each of those factors would be hard to figure out for an individual. I don’t necessarily encourage people to be right at the top of the zone. It’s far more important to train consistently and frequently, so that you have a generally high training volume. What might be most established in the literature is that a high chronic training volume below AeT has the biggest effect on aerobic adaptation. Starting workouts with lower glycogen levels is suggested to be the best way to promote mitochondrial biogenesis and other major factors in improving aerobic fitness. Doing this with too much dietary manipulation (e.g. keto/fasting) would likely preclude good recovery and higher training volumes, although this is probably very individualized. It seems more logical to set up conditions to get more training volume and have appropriate recovery. We have a lot of discussion in the general forum about this.
Edgar: Raising AeT can mean raising the AeT HR and/or AeT pace. AeT HR can go up, but we don’t want to see that trend occur at the same workload. We’re not concerned about AeT HR as a singular metric. As long as AeT Pace is higher, it’s implied there’s an improvement in fitness. That can occur with or without AeT HR increases. If an athlete has improved their training strategies to specifically target aerobic fitness, and trains consistently for several months, we’ll likely see that they no longer have cardiovascular drift at the previously measured intensity. This could be due to improvements in muscular strength, efficiency, fat adaptation, etc, but the resultant outcome is that cardiac stroke volume doesn’t decrease at the previous workload so HR doesn’t need to increase to compensate.
It’s not uncommon for us to see individuals who have little change in AeT HR, but with good training we’ll see that they are doing their aerobic threshold tests at a steeper grade and/or faster pace.
With targeted training, you’re likely to increase your AeT HR and/or AeT pace, but as a mountaineer, what’s really important is being faster at your AeT.