@bbarrera I wanted to comment on your post right after seeing but decided to wait until today to ask how is your fatigue level after this workout? More, less, same vs the typical VO2max workout you would normally do?
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Iâm thinking about turning a classic 4x8min. interval into a hard start and hold session to stay at Vo2max. I think I can digest the 8 minute chunks a little easier mentally.
Last night I did Jepson, which is 4x8min. with sprints in the middle, at 150%, but only 5 seconds.
I was able to do each interval 20w over my FTP, so around 107%.
For next time, Iâm thinking if I started each 8min. interval with a hard start, say 140% for 90sec. and try to hold 105 to 107% for the remainder, this should keep in V02 for most of the interval.
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So these hard-start intervals seem to be great for spending lots of time close to VO2max, but does the lower average power output mean we lose some other adaptations? I.e. whatâs the effect on time-trial performance or completing several high power intervals as in a road race?
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@Anna_K, yes, thatâs the correct question. Does increased time at VO2max improve performance? Or maybe more specifically does this type of VO2max work improve performance? I donât think there is a formal answer to that question. What weâre talking about in this thread is just a more efficient way to accumulate sustained VO2max minutes.
At the moment, I am going to say that descending/lower power intervals will not degrade adaptations. I"m sifting my way through a study of ischemic heart patients who reach 100% VO2max @LT (vs ânormalâ subjects reaching 85% VO2max @LT) w/ both attaining the same speed pace. What this meansâŚnot sure â yet!
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Yeah I know, but since people already start thinking about implementations⌠I threw in my doubts 
. I guess Iâll personally mix things up and do some hard-start intervals and from time to time some traditional constant-high-power intervals.
Too short to generate much fatigue, it was a 35-minute / 66 TSS race where I blew up and ended up off the back but didnât give up. Felt like someone had scrubbed my lungs for a day or two or three. And it was near the start of last yearâs allergy season and I hadnât started taking allergy meds.
indeed! ^^^
Can you send a link to that study?
Great question. I wish we had an answer! But letâs speculate.
We can consider âintensityâ (%VO2max) and âworkloadâ (power output) to be different stimuli, or at least different components of the metabolic cascade between inhaling O2 and pushing down on the pedals. The question is then: will we improve our performance more by optimizing for workload, or for intensity?
VO2 measured at the mouth reflects systemic O2 uptake, not necessarily directly related to power output. eg. for the same power output we can increase VO2 by raising cadence. That is to say higher cadence will raise intensity at a constant workload (lower âgross efficiencyâ), and vice-versa.
The excess VO2 might be due to the faster fiber contraction speed, or it might be going toward stabilization and accessory muscle activity. I just wrote about what VO2 & SmO2 tells us about biomechanics and muscle recruitment on the trainer vs on the road).
To get even more specific, I would suggest power output is only an indirect measure of internal workload, which may be more relevant for driving adaptations. Our mitochondria can consume some amount of O2 (VO2) to produce energy (internal work) to perform mechanical work (power output).
Maybe we want to improve how much O2 we can deliver to our mitochondria by optimizing intensity and %VO2max?
Maybe we want to improve how much O2 our mitochondria can extract to produce energy as ATP, maximizing internal work?
Maybe we want to improve how efficient our mitochondria and muscle contractile elements are at converting that O2 into ATP, and ATP into mechanical work, maximizing power output?
What are some of the implications of these Billat or LisbĂ´a Hard-Start intervals vs evenly-paced intervals (and vs intermittent intervals, to refer to the other thread) on these components of the metabolic cascade?
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Blood lactate threshold in some well-trained ischemic heart disease patients
- VO2max @LT: 99.8%
- HR @LT/VO2max: 93% HRmax
- Observed VO2max eliciting interval: >35 minutes (15min is just a warm-up!)
Itâs interesting in that itâs possible for energy systems to adapt in such a way, but unless you are in the IHD camp, not something to shoot for.
Published 1983 so there might be more modern studies available? 
(previous posted link may not work, try this one: http://scholar.google.ca/scholar_url?url=http://www.academia.edu/download/44270475/Blood_lactate_threshold_in_some_well-tra20160331-338-139eymj.pdf&hl=en&sa=X&scisig=AAGBfm1vEjhl4-QBmLMXmvjHDEUa_mmoOQ&nossl=1&oi=scholarr )
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Yeah - giving yourself coronary artery disease isnât a good way to boost fractional utilization!!
Next level marginal gains. 
Plus, their VO2 flatlined in efforts greater than LT/FTP. The trained IHD crowd had a VO2 comparable to an untrained individual.
Just something to think about if you question getting VO2 adaptations at lower power levels. The almost 40-year old answer is âYesâ.
Isnât it the other way around? They run fast despite their heart disease due to their muscular endurance?
They run fast for a person w/ heart disease, yes, but itâs unclear (c.1983) as to the contributing factors. Their LT is normal but their VO2max is compromised, so comparatively they run slow yet still trigger the VO2max adaptations.
(previous posted link may not work, try this one: http://scholar.google.ca/scholar_url?url=http://www.academia.edu/download/44270475/Blood_lactate_threshold_in_some_well-tra20160331-338-139eymj.pdf&hl=en&sa=X&scisig=AAGBfm1vEjhl4-QBmLMXmvjHDEUa_mmoOQ&nossl=1&oi=scholarr )
Is their VO2 any higher than if they didnât run at all?
No. Itâs substantially lower. Through training (mostly Threshold workouts) they raised their VO2max by 42% but was still 22% lower than an equivalent healthy cohort group.
Apologies for derailing the OP.
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Here is a little more data supporting extended VO2max intervals at powers that are much, much less than what are traditionally considered to be VO2max power levels. In this case, as in the Bilat case, VO2max is maintained for minutes at a time at powers that are below, at, or just above ~FTP.
Iâve heard people say, âIf youâre at or below FTP you canât be at VO2max.â While I understand how somebody might reasonably concoct such an unsupported hypothesisâŚthere is a lot of accumulated data that prove that assertion wrong. If you do it correctly (hello all you hard start interval fans!) VO2max can certainly be maintained for a LONG TIME while work rate is held at or around FTP.
In the study I took these charts from they asked participants to do two ramp tests. The first was a traditional ramp test which they called âCITâ. The second used VO2max data from the CIT & manual adjustment of work rate to hold participants at VO2max after VO2max was achieved. The kind of thing thatâs so tortuous it makes you wonder how the study made it past ethics review. 
Also worth notingâŚmost subjects in this study achieved a VO2 plateau during the traditional ramp test. Somebody once told me that if your VO2 plateauâs prior to failure on a ramp testâŚthen something is wrong with your heart. Well, for some participants in this study VO2 reached a plateau prior to ramp test failureâŚfor some it did not. So I can see how you might come to that misinformed opinion if you arenât used to looking at a lot of dataâŚmaybe if all youâve ever seen are your own tests or something. Definitely, though, subjects can reach a plateau in oxygen consumption, continue to pedal at that plateau for some time, then be unable to continue the ramp test.
Just some interesting stuff that made me think of this thread.
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Would you please share a study name or link?
A new incremental test for VO2max accurate measurement by increasing VO2max plateau duration, allowing the investigation of its limiting factors
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Iâve noted when I up the intensity that initially my HR climbs but after a while it can drop even though the intensity hasnât. Itâs almost as though it takes a short while to get to the optimum operating conditions when it comes to oxygen demands of the muscle.
I wonder if itâs to do with muscle motor unit recruitment. That as you spend longer at an intensity the motor unit recruitment changes. If fresh units are brought in to replace or supplement fatigued ones that oxygen consumption requirements go down. So in the ramp test although more power is being demanded it changes the motor unit firing and thus oxygen demand. Thus they can make more optimal use of units available from the oxygen that can be supplied.
You can imagine a signal from brain to muscles going âRight this is as much oxygen as youâre going to get, so Iâm going to change things a little to eek just that little bit more power for a bit longerâ.