Let me start off by saying that it is my opinion that HIT doesnāt lend itself to long-term planning and is best suited (again, in my own opinion) as a short/moderate-term block within a training cycle.
If you look at the 4 progression models I mentioned, 1 of them can easily be applied to HIT (progression by rep difficulty), 2 can be applied to a limited level (progression by load and RPE) and 1 canāt really be applied.
Load progression is the traditional HIT progression model (at least in the original Arthur Jones model) however it is limited in effectiveness (or rather how long it can be sustained) because with a single work set itās kinda hard to use the double progression model. Well, you can, but progression in load will still become quickly unsustainable (i.e. the more sets you do, the longer a double progression model is sustainable).
With either a single set double progression or a good old progressive overload/beat the logbook approach you will likely be able to progress for 4-6 weeks before you the wall. Less if you are an advanced lifter. And pretty much only on multi-joint exercises (you will likely progress for less time on single-joint movements).
The way to circumvent this is doing what Dante Trudel/the DC method calls for: when you canāt progress on an exercise anymore, you change that movement for something else.
The RPE progression can also be applied, but slightly differently. With super low-volume training yu absolutely must push your work sets hard. To the limit or very close to it (or even beyond). So a āpureā RPE/RIR progression doesnāt really work because, for example, sets with 3 (or 4) RIR shouldnāt be used with HIT training. Even sets with 2RIR arenāt going to work well.
So you canāt really go from 3RIR to 2RIR to 1RIR to failure. Rather you must use either one of these approaches:
Intensive RPE progression: Start at 1RIR, then go to failure, then beyond failure (e.g. rest/pause) then even deeper past failure (e.g. double rest/pause or rest/pause + drop set). Thatās still limited though. I donāt see this working long-term without burning out.
Methods progression: Here you stay at 1RIR - to failure most of the time but in gradually more demanding methods. This is actually a form of rep difficulty progression. But this also offers a limited progression duration.
As you can see, the main issue is that with HIT you are kinda painting yourself in a corner by having to always push very hard, which can become draining.
Whereas something like volume duration can be a break for the nervous system by allowing you to keep progressing even from sets with 2-3RIR.
But even volume progression is limited.
The secret to long-term progression is thus to cycle through the progression approaches.
For example, 4-6 weeks of volume progression; 4-6 weeks of progressive overload; 4-6 weeks of rep difficulty; 2-3 weeks deload then start over (I donāt like to use RPE progression).
In that sense, it can also be applied to HIT, but Iād likely make the blocks a bit shorter.
Something like:
3-4 weeks rep difficulty; 3-4 weeks progressive overload; 3-4 weeks; 3-4 weeks intensive RPE progression; 3-4 weels progressive overload; 1-2 weeks deload and start over.