My recollection of the original billat study which i thought was 30/30 intervals, found that the athletes could get a fair amount of time at/near vo2max while having less sustained time at their associated vo2max running speed and thus less musculoskeletal stress than doing longer intervals at that speed.
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I knew a very fast runner from Switzerland who during his lunch break would run a couple miles to the track, do 3k of “straights & bends” (fast turns, cruise the turns) and then run back. That 3k would be around 8:30-8:40. Then he’d do the real workout later that day. 
And of course there is the Oregon 30-40s (continuous 200s).
30/30s just work. Yes, you need longer intervals, threshold, etc. but they have been a staple in a range of sports for a long time!
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While I think you are correct regarding the original research and the idea behind it, I thought that 30-30s address a different part of system that contributes to VO2max performance. You can fail VO2max workouts in different ways, you could run out of steam (= energy) or out of breath. And I thought billats focus on the former (= anearobic capacity). Of course, nothing it binary here.
Again, that’s just a vague recollection, and I don’t even remember where I have read it. I’d be happy to be corrected — or to have further links.
In any case, it’d surprise me if the purpose of billats was to serve as an opener for longer VO2max work. I find billats easy and really like them. They are probably my favorite hard workout type. Long VO2max intervals are definitely not.
In the original study, three of the individuals were able to complete 22-27 of these efforts and spend 18+ minutes near VO2 max.
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Sounds like vo2 max.
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IIRC, research showed they were much of muchness, but Ronnestads could result in more time at vo2 max.
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As you said, it’s not binary. Usually pure anaerobic capacity efforts have much longer recoveries between the intervals to allow nearly full recovery and thus allowing you to go much harder during the intervals. Anaerobic capacity efforts could be something like 5 x 30s (all out) with 5 min recovery between.
30/30s are somewhere in between of pure VO2max workouts and pure anaerobic workouts mentioned above. Yes, the first few intervals are mainly anaerobic but once you extend the workout further and further the intervals become increasingly more aerobic (and power decreases).
Also, it should be noted that human body is aerobic in nature. Even if you produce energy anaerobically for a short period, the lactate clearance and ATP restoration is done aerobically - this is why 30/30s will stimulate both energy systems. Usually 30/30s will feel harder for athletes that have a high anaerobic capacity and likewise easier for “diesel” type athletes. Big anaerobic tank allows for harder efforts → larger oxygen debt → feels miserable.
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One way I tried to handle this, is get to a point where breathing wise seems unsustainable, like my chest will explode anytime if I keep at it, then I would lower the effort just a tiny bit, to maximize time at this “ragged” state.
Long climbs are good for this. What can be done indoor is limited, for me anyways.
That is true. That’s why I said I use them to introduce intensity, not to train VO2max. One or two sets of 30/30 or 30/15 depending on the person just to get them ready for harder stuff. I don’t do it with everyone, but I see that it helps a lot of people, especially my older masters guys, get primed.
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If they are proscribed as Billat did, then I think they have the desired effect on maximal oxygen uptake etc. The problem arises when people are given a 30/30 workout at a fixed percentage of FTP such as 120%. Plus there aren’t enough intervals to move past the initial anaerobic component. Done in resistance mode and go as hard as you can sustain with sufficient intervals for your current capacity and you’ll soon reach the breathing state covered above.
Is this at a stage where we bring up the HIDAT style of intervals researched in 2022?
I have done some really hard workouts… with some really fast people. I don’t think a VO2 max has ever left anyone gasping or breathing like a “fish out of water.” No doubt VO2 workouts can really, really hurt… but if you are going to this point I don’t think you are doing it right.
This is an excellent article that compile research from some of the most renowned researchers in the field.
The article boils down this knowledge into to main points:
- Accelerate the way in which we could reach 90%VO2max
- Continue to maintain 90% VO2max as long as possible
This take a fair bit of pacing and pushing one’s heart rate excessively high just limit the time one is able to continue the workout.
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Really great article and multiple good concepts I never see in TR workouts, so I often find I either waste a ton of the workout reaching a vo2max state on shorter repeats or on longer ones they are just impossible to finish unless I treat it more like a hard threshold repeat and pace conservatively.
The hard depleting start and declining intervals make a lot more sense especially for anyone with strong 1 min power but proportionately weaker vo2max like myself.
I may try some of those suggestions on next 30/20 set by just blasting the early warm ups a lot harder to clear AC, no erg, overshoot power on first few to get HR up fast and just do what I can to push through rest of set at high cadence, whatever the power is. Pretty sure it will do more than any stock TR VO2 workout has ever done for me.
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I have a favorite, suggested by Jespen Bondo Medhus that I tweaked a little bit:
I’m probably gonna get a lot of push back since I’m not killing myself, nor recommending anyone doing so, during VO2max workouts. There’s a workout later on as well - fatigue management.
Rather in line with
…but I guess you are correct 
Seriously, there is a slight slope to the threshold that makes it mentally manageable. Heart rate usually stays the same (just above 90% ) during that part. It is usually possible to do a third interval adding even more work above 90% if you’re up for it.
Fair enough… but to me deep, labored breathing after a hard effort is not “gasping.” If you are struggling to take a breath or your breathing is out of control (the definition of gasping) you are not doing VO2.
But if “deep breathing” = “gasping” for you than I guess we are just getting caught up in definitions.
The issue is if you just say “deep breathing” then that hardly captures the difference between controlled deep breaths from threshold-ish efforts and the “fighting to catch breath” VO2 breathing. Either that or I’m doing VO2 wrong too 
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If you fighting to catch breath during vo2max workouts how do you describe you breathing during set of anaerobic intervals?
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115% sounds way too low for 30/30s. I would think you’d need to be at like 130% minimum to get results. I don’t think I’d get anywhere near max HR with those.