For Training Peaks, the “threshold” number to enter in your Settings is 170. Everything in Training Peaks references the anaerobic threshold, not the aerobic.

AnT isn’t the best benchmark for training, but it’s probably ideal for measuring fatigue. With the TP threshold set at AnT, CTL and ATL will be good measures of training stress.

Have you thought about doing one more test at 153-155? You might not even be aerobically deficient and it would change what zones you spend your time in.

Like Rachel, I suspect you don’t have ADS. When you find a pace where your HR drift is less than 5%, I suspect your heart rate will be higher than 150, perhaps even in the 160s.

There’s no such thing as “too easy”, especially when you’re talking about 5-10 beats. If your AeT is 150, then 145 is 97% of AeT; 140, 93%.

When your AeT and AnT thresholds are very close, and when the speeds are very fast, then a 10-beat difference may have a very different training effect (and you’ll be able to feel the difference). Until then though, I wouldn’t worry about it.

Does this mean I should be able to run “easily” e.g. 2+h at my AeT?

Not necessarily. For people new to training, the gap between AeT and AnT is usually quite large. With an undeveloped (or damaged) aerobic system, AeT will be quite slow. So new athletes can do almost all of their training at AeT.

As athletes get fitter, the two thresholds converge. This usually means that AeT rises to meet AnT. It does so first by heart rate and then by pace.

Once AeT and AnT paces are relatively close together, AeT is no longer “easy”. It’ll be almost as fatiguing as AnT work. The metabolic cost is low (~2 mM), but the neuromuscular fatigue is high.

For example, I spent the first three years of my skimo training at AeT almost all of the time. By the fourth season, I just couldn’t tolerate the volume at AeT, so I had to train slower. And then much slower as my top speeds got faster. The good news is that once AeT and AnT are close, AeT training doesn’t need as much of a stimulus as it did in the beginning. Training slower will support it quite well.

If you use Training Peaks to track your training, this is where their metrics really help because they’re based off of AnT. The TP metrics are not ideal for describing fitness, but they do a pretty good job of gauging fatigue.

TP always measures fatigue based on AnT, so as AeT rises, the fatigue in Training Peaks from those workouts also rises.

Does that make sense?

P.S. Is there a lab near where you live that you could get a lactate test done? You seem serious enough about your training that I think you’d benefit from knowing exactly where your AeT is.

Great! I’m glad it helps.

I was really confused when it started happening to me. I thought things were going horribly wrong when in fact it was the opposite.

Basically, with a lot of aerobic training Zone 3 will narrow–as Zones 1 and 2 grow–until it’s almost gone. You can see this on lactate curves as the inflection points get compressed toward the higher intensity part of the chart (on the right-hand side).

Then things get really interesting as you can start to develop different “gears” above AeT for different types of events. For mostly steady-state events longer than two hours, you want AeT as far to the right (at as high an intensity) as possible. And an ultra-athlete may not be able to tolerate much time at all above AeT.

For events shorter than two hours or those that are more stochastic, you want a flatter lactate curve above AeT to make time there more tolerable. (But still having AeT as high as possible.)

But anyway, that’s a rabbit hole for another time…