Hey hey, we are currently recording a series of VO2max episode, and we would LOVE to answer your questions! 
Simply: reply to this thread!
Best, MJ
Should you be going āall outā each interval, or leave a little in the tank? Related, what are the differences in adaptation and stress between the two highest zones (6 and 7)?
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Thank @cgamio - added to our list 
My Tuesday vo2 max sessions are usually 30/30s. With a focus on a hilly xcm event are these the best versus, for example, 5 x 5, 40/20s and so on. And how would we know whether to āmix it upā using the workout wizard, or āstay the courseā by doing the 30/30s.
Love your work.
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Great Question @Phil . Added to the list
MJ
I have heard enough bits and pieces of the answer to this in the podcast and here on the forum to have a good idea of what the answer will be but I would love to hear it all put together (Iām still catching up on the podcasts, so perhaps itās in an episode that I have yet to get to):
For the running 30/30s, when picking out terrain, what is the most important aspect to consider? Is it that the interval be performed on a hill, as is suggested in the workout? Is it that the rest period be limited to 30 seconds? Is it something else such as consistency (all intervals on similar terrain instead of a mix)? What are the trade offs of doing 30 second intervals with 45 seconds rest to ensure the intervals are up hill vs. keeping the rest at 30 seconds and perhaps performing up to half of the intervals on flat terrain?
ā
Context: my area is near the coast and our terrain is small rolling hills. The biggest hill within jogging distance from my house is one which supports about 4 intervals (run 30s up, turn around, walk 30s down, turn around, repeat) before Iām at the top (since I travel further during the uphill interval than during the downhill interval). At the top I have maybe enough flat terrain for a 30s interval (100-150m) before Iām going down the backside of the hill and can do the remaining intervals on this flat terrain at the top. The alternative is to take 45-50 seconds for the rest interval to ensure I get far enough down the hill that I donāt reach the top before the end of the set. Or to use the ample flat terrain around me to ensure consistency in all intervals.
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Iāve recently returned to the 30 / 30 short HIIT format having been doing 5ā Long HIIT this past year on the bike. I am finding that the 30/30s donāt raise my heart rate as much as the 5ā intervals. Primarily because it recovers well during the 30 seconds off I think. Should this concern me, or donāt worry as there are other physiological benefits being induced?
Hereās a sample 30/30 HR trace from an outdoor execution. The new improved AI coach seems happy that I nailed it.
Same - I have a great hill at home thatās perfect for 5-7 intervals but any more Iād be going over the top; also when visiting family out of town itās super flat, with a tiny hill (aka a park that has barely-there-contouring). How best to do the all-outs on flat or descending w/o injury? Should we slow down?
Another unrelated question: when NOT to do 30:30s? E.g. when your HRV or sleep or recovery arenāt good, should we still do them? Pretty sure I know the answer from our live HIIT sessions, but would be nice to include some insights on when to call it and when to push it.
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Another question (but I think the episode may have come out today): I was listening to an older user questions episode and there was a question about doing aerobic workouts in your race modality (I think it was trail running) and doing the VO2max workouts in a different modality (in this case it was rowing). If I understood it correctly, in terms of VO2max benefit the modality shouldnāt matter. If youāre a runner and do VO2max or HIIT workouts on a bike, in the pool, or on an rowing machine, you will get similar benefits in terms of VO2max. Question 1: did I understand that correctly?
Question 2 (may not be strictly VO2max related): If I did understand that correctly and Iām training mostly for 5k and 10k running races, what is the tradeoff if I do my 30/30s on an indoor bike? Are long aerobic runs enough to build running form efficiency? Are the strength and conditioning sessions enough to build running strength? Or is the best approach to stick with the adage that āto run fast, you have to run fastā ? Hope that makes senseā¦
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I know that Athletica favours the 30-30s for intervals for improving VO2max. However I note that the research this is based on is cycling research, and I wonder if there is also research to suggest that with running, this is more effective than other interval training structures that seem to be a lot more common. I am a little concerned if we are generalising from cycling only, as the neuromuscular demand is so much greater when getting your HR to this level when running. For someone who is a relative beginner to speed work, the very first interval training session Athletica gave me was 10 x 30/30 intervals on a hill - and it wanted me to do 3 sets of this! I managed 9, split into 2 sets, before near death. In addition, it had also prescribed 5 or so strides to do at around an L4 HR prior to the intervals. This also strikes me as strange; wouldnāt our strides be better off in another session in the week, at the end of an easy run? Wonāt doing the strides prior to hill intervals compromise the efforts in the hill repeats, especially for a less experienced runner?
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Thank you Alyssa, great reflections!
There are ways to lessen the neuromuscular load (uphill/grass) while running. But you are correct in thinking.
Those strides before hill sprints are there to prime you, allowing your fast twitch muscle fibers to be primed and ready for the efforts that are to come.
Those are short 10 s pace pick-ups, and they are so short your heart rate doesnāt really rise all too high. But if they are too much for you; maybe do every other one?
3x10x30/30 was your first 30/30? Sounds like a bug to me. I am so glad you shortened it. Near death is definitely not what we want with theseā¦ hit the target, leave 1-2 repetitions in the tank, walk away.
Great if you can share a screenshot of the workout so we can investigate. Are next ones more reasonable?
MJ
Hi Marjaana,
Thanks so much for your feedback! I will post the screenshot of the first interval session blow - prescribed and what I completed. Yes, my next interval session was prescribed 3 weeks later and is coming up this week, and is much more achievable at 1 set of 5 30/30s.
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Perfect. Yes, that looks much more reasonable.
I think the AI is trying to keep you progressing within your time constraints, and gave you a bigger workout, thatās not great from AI but always have a think 
does this make sense to do? Is there a too big of a jump from previous set?
If next one goes well, you may add one or two reps the next time. But asking 3x10 is a bit naughty of AI.
Youāre doing great!
MJ
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In the recent vo2max podcast there was mention of breath trainers for vo2max improvement. Do tools such as Airofit or power breathwork & what is the science behind this?
Thanks