RPE scales seem to be pretty well correlated with heart rate especially for experienced (and mindful athletes). Lot’s of studies out there. Besides, heart rate does not capture the eccentric muscle strain in downhill running, or lack of it in uphill running.

how might I approach approximating my AeT and AnT using ventilation/RPE?

Not sure if read the series on Monitoring Intensity I shared earlier. Part 2 of the series has the information you are looking for.

This article also lists different methods to determine AeT/AnT and pros/cons of each approach.

Scott answered a similar question here.

how can I tell if and when to add some structured intensity into my walking, running, and hiking training?

Once you find a test that works for you, repeat the AeT/AnT test every month or so (depends on your training volume) and see if your AeT is within 10% of AnT. If it is, then you can add some high-intensity workouts to your training.

Related to that though, if you’re using (calibrated) ventilation as a limiter, then that should work, especially if it’s tied to cadence (steps breathing in/out.)

Can you elaborate a little about your second post? I assume that when you write “calibrated ventilation” you mean using a HR monitor to define zones, figuring out my ventilation feel/pattern at each zone, and then applying that?

Yes, via an HR monitor or lactate samples, but I understand your hesitation, so…

…what do you mean about matching breaths to cadence? Can that even work on uneven terrain, for example, a single track hiking trail?

Yes, I’ve been using this for years, and it’s very reliable once you know your own rhythms. It’s especially helpful during races when it’s easy to go too hard too soon. I think of it as a “poor man’s power meter.”

But… as you suggest, it depends on terrain. When the movement pattern or terrain changes, often breathing does as well. Try these:

For flat running:

* Zone ~1: 4-steps-inhale, 6-steps-exhale
* Zone 2-: 4-steps-inhale, 4-steps-exhale (easy effort)
* Zone 2+: 4-steps-inhale, 4-steps-exhale (moderate effort)
* Zone 3-: 3-steps-inhale, 3-steps-exhale (moderate)
* Zone 3+: 3-steps-inhale, 3-steps-exhale (hard)
* Zone 4-: 2-steps-inhale, 2-steps-exhale (hard)
* Zone 4+: 1-steps-inhale, 1-steps-exhale (very hard)
* Zone ~5: Breakaway breathing, no rhythm possible

For uphill running (or skiing): (roughly half of flat terrain rhythms)

* Zone ~1: 2-steps-inhale, 3-steps-exhale
* Zone 2-: 2-steps-inhale, 2-steps-exhale (easy effort)
* Zone 2+: 2-steps-inhale, 2-steps-exhale (moderate effort)
* Zone 3-: 1-steps-inhale, 2-steps-exhale (moderate)
* Zone 3+: 1-steps-inhale, 2-steps-exhale (hard)
* Zone ~4: 1-steps-inhale, 1-steps-exhale (hard to very hard))
* Zone ~5: Breakaway breathing, no rhythm possible

I always use this in races, because start line jitters raise HR and everyone starts too fast. For a skimo race, I start at 2/2 for the first ten minutes (usually at the high-end of AeT) and then move to 1-1 for most of the race. for the last climb, I abandon breathing and go as hard as possible.

That’s great news. I’m glad that it helped.

I was thinking more about this today and thought that the synchronization is probably based on two factors: the recruitment necessary for the movement pattern (steep terrain recruiting more muscle fiber than flats so increasing the demands) and the steps-per-minute (SPM or, in cycling, cadence at half the SPM.)

I found that on the less steep sections of long variable climbs I often had to hold myself back, staying at 2/2, even though I could have gone faster, knowing that, if I did go faster, I would have to slow way down, or even stop, once it grew steeper again. By staying at an even 2/2 pace, and even slowing down to 1/1, I could keep my effort steady all the way to the top.

That’s one of the qualities that I find really helpful. There’s a lot less lag than there is with heart rate, so with more real-time feedback, it’s pretty reliable to hit a rough intensity target.

One exception is that after a high-intensity effort, the synchronization will totally change as the CV system catches up. This is really noticeable during recovery intervals in intense workouts. But again, it’s also good feedback that says that the load is still being absorbed.

Going downhill, of course, my HR dropped. I don’t have the leg strength and joint stability to run downhill fast, at the speed I would need to maintain my HR. Instead, I alternate walking and light jogging on the downhills, knowing that my HR will go down, but saving my body from injury.

This is normal. I just breathe normally (at random) when going downhill. Trying to put out enough effort to make synchronized breathing necessary would kill your legs from the eccentric loading. The local effect on your thighs would be way higher than what your ventilation would suggest.

Another similar example is when really fit mountain athletes try to run in the flats to stress their CV system to the same extent that they would be going uphill. They often don’t have the strength endurance to withstand the pounding and end up with very sore legs afterward.

I’m glad it helped. It can be quite meditative as well. I never use headphones while I run, so the combination of silence and synchronized breathing can be really great thinking time.