I'm not trying to invalidate HR training at all. I understand the benefits of autoregulation using HR training. I just thought there might be a different measure of aerobic function other than the time to go a certain distance at a given heart rate due to the significant variability of it.
I get that. Unfortunately, I'm only aware of a couple "tests" - exhaled CO2, blood lactate, VO2 max ... All of which require a lab. If you're not training to a heart rate, I don't see how you could assess whether you were staying aerobic.
And this may just be where I'm just out of my depth! I think aerobic function and heart rate are entwined to an extent that you can't separate the two like that; variability in your heart rate IS variability in your aerobic system.
If you want to rule out the improvements just coming from skill or environmental fluctuations, you could try this: Train with whatever modality you want (e.g. running), using HR as your guide. Once a month, perform a MAF test indoor on a different modality (e.g. cycle). Keep your sleep and diet as similar as possible the day before and during the MAF test. Provided you haven't been practicing your cycling, any improvements you see should be due to aerobic increases.
My main concern here is that you may not be skilled enough to be able to actualize aerobic improvements in a different skill. If I only cycle once a month for the MAF test, I would be concerned that if I didn't see improvements it could be because I'm bleeding energy from a million points due to gross inefficiency.
You can also use this with rucking. Rucking has been found to increase running ability, but running doesn't seem to increase rucking ability (or it does, but only to a certain point/weight). So you could train via rucking in zone 2, adjusting weight and speed to maintain your HR, and then test in running. So here you could train with rucking and test with a MAF test run.
Honestly this reminds me of Al's "
Simple Endurance" protocol - test before, then just swing for a month, test after. The training is dissimilar to the tests, so any improvements in the tests would be attributed to improvement in physiology not skill. The main difference is in his protocol you aren't using HR as a guide, and the test is a MAF test. Both are easily modified, so I could easily see this become an unholy hybrid of his simple endurance and
his heart rate training combined into one - so you perform the simple endurance protocol with a bell that allows you to meet the heart rate training requirements, but rather than performing them OTM you end up just having "session time caps" - you swing like he describes in his HR training article, but for the total time as he lays out in his simple endurance article.
Again, I don't think this is what you're looking for because you're still "limited" by your heart rate and its variability, but it would allow you to train and assess while minimizing any skill component.
Sorry for the long post and rambling... I enjoy this train of thought and the conversation, and its early and I have coffee...
Sadly the coffee just ran out, so its time to go train! (Wait that's not sad...)