Is >90%VO2max the only thing that matters when doing intervals?

I trying to understand the difference between long and short intervals. I have two examples. First one is Dicks -2 (4x8 min 105%) and the second one is Taylor -2 (42x30 sec 120%). When i did both of this workouts the time in 90%VO2max bpm is way different.

Basically with Dicks -2 time in 90%VO2max was 27 min and with Taylor -2 time was only 3 min. So what i want to know if % of FTP matters or is it only time at 90%VO2max bpm that is important? I thinking that pushing pedals harder would be good? But when browsing the forum it sees like that only 90%VO2max is important?

Both workout had my legs empty at the end. I post some pics over power and bpm from Strava.


With VO2max intervals, it’s time @>90% HRmax. Now for a few notes:

  1. VO2max is a physiological process, not a power/wattage target.

  2. The >90% HRmax is a pseudo-proxy for this process that correlates reasonably well for most people.

  3. TR’s literature states:

VO2 max power is basically just the wattage you can output while riding at VO2 max. It’s your power output when you physically cannot uptake anymore oxygen…pVO2 max falling around 118-128% FTP.

  1. Unless you do a lab gas exchange VO2max test, you won’t know the exact HR/%FTP of your VO2max process. That common 120% FTP is just a best guess (remember the 118-128% from above?).

  2. You can and will still illicit VO2 adaptations at lower HRs, even Z2 rides work the VO2 system, it’s just that the >90% guideline is the optimum range.

  3. VO2max kinetics is basically how fast our bodies respond to the process. It can sort of be represented in exactly the way you showed: short vs long intervals. If your HR never gets up to 90% during short intervals then you most likely have slow kinetics (pros most likely have fast) and longer, constant power intervals work better for you. Kinetics are somewhat trainable but I don’t know if you want to chase that undertaking.

  4. Try Rattlesnake.



This is an issue I also face, so it seems I am a slow responder.

I know I need to work on my VO2, so I jumped into some appropriate workouts. Was very proud of myself after completing them, only for a buddy to tell me I’d spent very little time at VO2 HR.

I also tried Rattlesnake and as I knew I’d have trouble getting the HR up, I went the whole hog with Rattlesnake +2. Managed to get my HR up into VO2 territory only in the last 12min block of work.

I also tried Elephants, which I completed, but again time at VO2 hr was minimal…i only got the HR up high enough halfway through the last 2 5min intervals. A lot of effort for not much VO2 goodness :joy:

Outside here it’s hot most of the time and I can get my HR up pretty regularly. So my next step would be to reduce cooling in my pain cave and see if that helps (and hopefully doesn’t destroy my parquet floor)

I’ve started doing VO2 max intervals in erg but adjusting the intensity on the fly so my heart rate stays at approx 92/93% of my max


Blockquote VO2max kinetics is basically how fast our bodies respond to the process. It can sort of be represented in exactly the way you showed: short vs long intervals. If your HR never gets up to 90% during short intervals then you most likely have slow kinetics (pros most likely have fast) and longer, constant power intervals work better for you. Kinetics are somewhat trainable but I don’t know if you want to chase that undertaking.

So i am better off doing 8 min intervals at 105% because of way more time in VO2max zone? Threshold workouts is VO2max training for me? And it means that 30/30 workouts for me is pointless?

I know about 30/15 workouts, but i am pretty sure i my legs would fail pretty early on because 30/30 was real hard for my legs from around the middle of the workout even if my heartrate does not show it.


Very interesting question, I have the same “issue” as Trhuster and would really appreciate more information in this subject!

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Watts @ VO2 max is a shifting target due to rate of energy demand – and rpm matters here, as well.

What does that mean? Ok, I haven’t done a hard, hard 4min effort for over two months. I did a six weeks of just going out and riding at 60% for a couple of hours, and then for the last three weeks, I’ve done a long 75-80 mile ride each week, and a sweet spot session of an hour at 90% FTP.

Now, I haven’t tested FTP – I hate tests. But, after 20 years of using powermeters, I know that an hour at a HR of 140 is 90% of my current FTP. Those sweet spot chunks were at 315w, so ok, 350-ish, down a little from the end of last season, which it should be.

But here’s the rub – I’m a slow twitch grinder, and my FTP tends to be a high % of my VO2, especially in Base. I was getting slow component VO2 at the end of those long rides, but reaching slow component VO2 at 85rpm and 220w is a whole lot different than trying to hit 370+ at 110rpm on my fixed gear trainer setup. So, last night’s 2min on, :30 off set was done at a damp-squibby 360w, and I was cracking at the end of each interval.

Simply, my old legs were not used to doing supra-threshold power, and not used to trying to do it at high rpms, so the watts were lower. But, as Andy Coggan says, sometimes “alls you can do is alls you can do.”

There’s something to be said, I think, by just doing the intervals at the highest steady output that your legs can do that day – and to vary rpm for those zone 5 intervals, rather than just doing them on the same hill every session, or in the same gear on the trainer. Just because you have the VO2 capacity doesn’t mean you can channel it to the pedals in all situations, at all force and rpm loads. Vary the stimulus.


I also have issue of getting HR up on trainer. Outside, no problem. I often read that our max HR is different for different activities. So my max cycling HR is different than max running HR. This is because more muscles are utilized during running. My theory is the same thing is happening while riding indoors vs out. I’m using less muscles indoors (less use of upper body) and therefore less demand on how high my HR needs to go. I could be wrong, but that relationship seems to make sense for me.

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OK, this is an eye opener (for me); does anyone’s HR ramp quickly enough to punch into vo2max HR zones in 30 seconds, other than perhaps an all out sprint? Or are these 30sec stacked so closely that it doesn’t get a chance to drop in the rest interval?

@MarkS i think not on a single run but during the whole interval it should. Below you see two intervals I`ve done in recent weeks. First is 30/15 at 130%FTP and the second picture is one set of 5 Min at 110% (with a starter at 120%). On both sets my HR ended up at the same level (153 bpm or appr 89% of MaxHR), but with two different ways to reach the goal. If on a 30sec leg the resting time i stoo long, you?ll probably miss the goal of the session. Target should be a raising HR over the time of the set, I think

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Not so sure about this, though it may appear that way if you are strava stalking pro data as they are in a high state of fatigue a lot of the time.

I would have though it depends it depends more on things like…

a) How developed the aerobic system is vs anaerobic abilities. (i.e. how quickly anaerobic resources are depleted).
b) How warmed-up the athlete is, and other factors affecting muscle oxygenation/vasodilation including supplements.
c) How much fatigue the athlete is carrying. (Depressed aerobic system => more anaerobic contribution => Slower kinetics)

Obviously b) and c) can vary for the same person over a short period of time… which is something I’ve observed in the past myself - cardiovascular response to intervals of a given intensity/RPE can very noticeably from one workout to the next.

You can also make the first interval a higher %. If im doing 12x30/15’s at 120% ftp, I’ll make the first 3 at 130%, middle 6 at 120%, last 3 at 110%. Still doesn’t get my HR up like it would outside, but my avg HR for the entire set is much higher than if all were done at 120%.

I’d use it as a very rough guide but not focus on the target too much especially if estimated as 90% max HR (though can be used as a ballpark for getting started). If you’re using lab equipment to measure VO2 you may well find that works much better.

Much like the 95%of 20m power = FTP myth, it relied on averaging results from a large group of athletes and doesn’t work that well for a lot of people on an individual level. It might get you in the right ballpark, but it isn’t gospel.

Secondly, the reliance on HR as the measure makes it very difficult to even compare different
instances of the same workout due to natural fluctuations. This is particularly bad in this application as we’re targeting a very narrow HR zone (getting above ~95%max HR will prevent most people from doing enough work)compared to the variance that many peopleexperience day to day. If you can do the same workout on 2 different days with 5, 8, 10bpm difference, it really doesn’t make much sense to make too much of the HR target, as those differences could easily be the difference between 20 minutes in the zone and zero, for the same work, RPE, respiration etc.

…and that’s before we get into how difficult is it to get a good estimate of max HR… and that maxHR changes with training and other things.

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Looking at some various workouts in the last few months shows a similar pattern to the OP:

For 30 second, 1, 2, 3 and 5 min hard efforts with equal rest time, it looks like for 30 seconds I don’t reach 90% of HR Max until many many efforts have been completed and even then for 15-20 repeats I accumulate very little time at target HR. Even when really blasting the efforts at 130-140% FTP. My HR just recovers too fast (yay!!).

1 min efforts get about 15-20 sec at target heart rate >150 bpm
2 min about 45-70 seconds
3 min about 1:45 - 2:10
5 min about 2:30 - 3:00

4x8 workouts if I target 110% then get a good 6:30 - 7:15 above 90% HRM. That’s a nice yield of time at target HR but these hurt. They hurt a lot. If I cut the recovery down to 50% of the work interval have a hard time completing a 4x8 workout. 1:1 is OK.

There are writings on hot starts and such, but if you have a high level of fitness and want time >90% HRM then need to cut the recovery for things like 30/30 or 40/20 or suck it up and do the longer intervals. Training aint easy!!

Hope the numbers are useful…


On edit - mentally, the 4x8 is hard. 5x5 is doable and even 8x5. 8x5 with equal rest is about 90 min of trainer time and would get about 20-25 min at target and probably a good trade between mental suffering and Time at Target. YMMV


I have two criticism’s of the way TR plans are set up:

  1. Threshold/SS workouts mostly stop at 4x20 and don’t push out to 30-40 min intervals.
  2. VO2 are prescribed at 120% of FTP.

I put this down to them, probably rightly, biasing the workouts to be completable to encourage long term compliance. Ultimately the best predictor on performance is going to be consistently executing any workout. If you can encourage people to do more workouts by letting them ‘win’ the workout, that’s probably for the best.

That being said I have had a huge amount of success doing ‘full gas’ VO2 intervals. Basically you are wanting to be cracking at the end of every interval with your power starting to trail off for the last 15s because you don’t have anything left. As long as you have enough that you’re able to get above threshold you didn’t cook yourself too much.

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Don’t have any answers, but I am interested in where this discussion goes, as whilst i currently stick to the TR VO2max workouts as described, i have also questioned in my mind the lack of maximal efforts built into them (other than tests).

I might have this totally wrong (happy to be informed) but my understanding of VO2 is increasing oxygen intake not HR. I dont understand the focus on HR as a target is extremely variable. HR shows the physiological demand and it lags power.

Besides power, would it make more sense to pay attention to breathing?

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HR is prone to sway with sooo many factors but…>90% HRmax is a good enough correlation for most people to be used as a pseudo-proxy for VO2max, even on those variable days.

And VO2max is a physiological process and not a power target (your VO2 kinetics are also going to lag power). You’re never going to enter a state of VO2max on the first pedal stroke. As the TR quote above states, pVO2max falls around 118-128% FTP. So how do you know if that 120% interval is actually your VO2max? Without an actual gas exchange test, VO2max is a tricky best guesstimate. We can use both HR and power to close in on the least fuzzy target.

I do believe the TR gurus have said that it’s ok to experiment and do some trial and error with VO2max workouts because it is such a fuzzy zone and everyone’s target is going to be different.

Your breathing at the beginning of the interval (assuming it’s a 3+min jobby) is going to seem like daisies and rainbows compared to the hacking, wheezing, gasping ragged affair that should be taking place at the end of the interval. It’s basically drowning on dry land. You shouldn’t even be able to think about anything let alone your fancy breathing stylings.

Have fun! :grin:


Absolutely yes, breathing (along with other RPE indicators) is a really key indicator of whether you’re getting in the right area if you’re in tune with your body.

Pay attention to breathing in the early part of the interval… if it isn’t getting pretty heavy (ie. deep and moderately fast) by 90s in then you’re not going hard enough.

However, if breathing is really ragged other then at the very tail end intervals then the likelyhood is you’re going too hard and won’t get as much quality work done as you could have. Breathing should be very hard but still (just) under control - find the edge just before where your breaths get too quick and become shallower. If you feel like you’re dying in the early part of the workout, then you’re probably compromising your ability to achieve an adequate volume of work, and are likely getting up in the >95% maxHR area. (more like Seiler’s 4x4m group as opposed to the more effective 4x8m).

Remember this is about training the maximum capacity of your aerobic system, not your anaerobic system.


Agree and this is very important. However, by the time someone is asking about time on target or time in zone, we presume they are past the consistency phase and are looking to optimize their training.

I see athlete progression as something like this:

  1. Rides regularly (enjoying a hobby, gets some fitness, etc)
  2. Starts training (committed to riding and improving)
  3. Follows a training program (training consistently with purpose)
  4. Seeks optimization of training program (assumes commitment and consistency and an objective)

It is perfectly OK for riders at any level of experience to bop back and forth between phases. Progressing from 2 to 3 is the big gain area. This seems like magic but it’s actually very simple. 3 to 4 is tough. It’s very hard to make additional gains for real world “Joe’s” with jobs who have been at level 3 consistently. I think this is where a lot of our complex threads come from. We are all looking for another 5-10 watts of FTP after 5, 7, 10 years of training solidly and seeking a new program that might do that (polarized v sst for example)

For me, when I am struggling with consistency, I look for workouts that are more fun to do. As a result I do too much SIT, HIT and race practice stuff in winter. I can do 3x20 or 2x45 but it’s boring.

But, when I’m committed to a goal and seriously training, I have to suck it up and do the really hard workouts that are not fun (4x8, 2x45) in order to get those gains. None of this is magic though so that’s the good part. Its all within reach for folks that want it.

TL:DR #1 - If you really want maximal performance it’s probably not going to be fun getting there. It’s hard work. But the rewards are bigger.

TL;DR #2 - If you really want lots of time in the >90% zone do a bunch of hard work with 5-10 min intervals. You’ll hate it until you get the result.