Disagree agree here, there is high individualism for power zones above threshold specifically VO2max which is well documented. It varies depending on the modality of the workout i.e duration and work rest ratio. Sure you can look at the data after the session and use it as a measure for the next but there’s no guarantees.
That often happens with hard start interval, whats wrong with this, you’ll still be at or near VO2max (unless you blow up and end up under threshold)
Not sure what you are disagreeing with. Point I am making is that with a power meter you can prevent the case that I am describing in the next sentence.
Back to the subject imo you want to leave margin of error for Z1 workouts maybe 70 - 72% but I agree with others thoughts that VT is a good way to check you are not going too hard.
Z3 work:- Threshold or VO2max just do them as hard as you can as long as each interval doesnt vary too much from the others, maybe use erg mode for the first to get a guage and then slope, or stay in erg mode and us the percentage up and down buttons as required.
Think I might have been adding to my post when you replied… the problem with dropping down towards threshold is??
Thats what happens with hard start intervals, it is a valid approach to VO2Max work, after all VO2Max is a state not a power or power range.
This is my thinking from combining bits and pieces of information over time, but happy to be explained otherwise:
VO2 max is when you are consuming the most O2 and converting that into power. That happens clearly at a level above Threshold and is very roughly at 120%-125% of Threshold power.
If you go very hard at the start and you fall back to Threshold power towards the last intervals, then you are not at the maximum rate of using O2 turning it into power. You would still be breathing much harder then normally at Threshold power, as if it was a VO2 max effort, but that would be more related to the build up of CO2 and your body wanting to get rid of it than the O2 requirement.
I’d tweak that slightly and say that it’s not that VO2 max equates to 120-125% of threshold, but that that’s a good number for doing VO2 intervals as it’s hard enough to get you into a state of VO2 max fairly quickly, but “easy” enough to allow you to stay in that state for a sustained interval. Doing 110% of threshold would get you to VO2 max eventually but it’s going to take a while so it’s not very efficient training. And 150% of threshold is going to get you there very quickly but you can’t stay there for long. So the purpose of hard start intervals is to go off a bit harder than 120-125% to get you to VO2 max faster, then drop the power to enable you to sustain that state. And as a happy coincidence, going off hard then settling into a more sustainable power correlates very well to a lot of race situations.
Interestingly on a recent podcast Chad said that you should be aiming to work at a high percentage of VO2 rather than VO2 itself. Might need to try and find that and go back for another listen as that was news to me!
Hypothetical question: 12x2min at 125% vs 5x5min at 115% in general? And for rider with high anaerobic contribution specifically?
EDIT: I am trying to decide which progression to follow for upcoming block.
Agree with this, which is why I was saying it depends on the modality of the session.
10x 1 min on 1 off at 125% might get you zero time at VO2max
4x 6 minutes might need to be at ~112% for some people to complete the set and might get you ~18 minutes at VO2max
Tom Bell suggest the primary metric to look at is heart rate between 90 - 95% of max.
I’ve got various running books that say adopt a pace that gets and keeps you HR between 92-95 precent of true HRmax, another says 92-97%
Edit: never seen higher than 97% suggested
1:1 recovery ratio or something else?
For me personal the 5x 5 would give me more time at VO2max.
Do both and see how much time your HR is over say 92% 
Yep, 1:1 ratio. But I guess your reply to @cartsman post actually already gave me answer – I personally spend more time at Z5 HR with longer intervals.
I’d say it partly depends on what kind of racing you’re going to do. E.g. if you’re doing events with hills that are going to take >2 minutes to climb, I’d do a progression which extends the length of the VO2 intervals. Whereas if you’re doing punchier races where it’s about accelerating and recovering then those shorter harder intervals are more specific.
If there’s no particular event in mind, then as a more anaerobic rider I’d be inclined to do the longer intervals to nullify your anaerobic contribution (you can “cheat” your way through shorter intervals with a high anaerobic contribution). Other options would be the hard start intervals and/or keeping recoveries quite short.
Thank you. I don’t race at all, only doing ultra-distance stuff (24h+) for my own pleasure. VO2max is just “necessary evil” to raise the roof 
Good point.
If you events are a long way off and say need more short efforts I’d move from the longer VO2 in base and build and move to the shorter ones in the 5 - 6 weeks before your season event.
Of course the opposite might be true for some people.
Two votes for the longer VO2max then, thats a shame, they are so much harder both mentally and physically (well I think so and I wouldnt say I’m that anaerobic, might be even harder for someone that is, not sure.)
Don’t forget the option of 3 or 4 8-minute intervals with a 2-minute hard start. Hurrah! 
Ok, challenge accepted, week after next will go for it, PL-wise it should become slightly less Stretch workout 
(2min at 121-125%, 6min at 106-110%, 5min recovery)
if I did the math correct ((239*.2)(260)+(239*.1)(660)) each interval draws down 14.3kJ from your anaerobic ‘battery’ and if you have a small enough ‘battery’ then you might fail to complete the first interval. And if your ‘battery’ is say 10kJ, then it would be a bad interval design, for you.
Thanks for that. So I was doing a bit more digging and this is what I make of it: I think that VO2 max is tied to a particular theoretical intensity, which is the power produced when using max amount of O2 without any power being produced anaerobically. It is just that the power produced is always a combination of aerobic/anaerobic, if you are fresh and just at that theoretical VO2 max power, there is still a considerable amount of power produced anaerobically. So you would not be at max O2 consumption, but would get there eventually when you get tired and anaerobic power decreases. This then ties in to your explanation that picking 125% makes anaerobic power decrease sufficiently fast to get you to VO2 max in a reasonable time. Also it is probably a good amount above the theoretical VO2 power, such that anaerobic power does not need to fully come down to zero in order to achieve VO2 max.
