Prescribing VO2max

June 11, 2020 – UPDATE

As an update into my current thinking, HR is simply too variable to be a reliable metric for internal training load near VO2max. Both the strength and weakness of HR is that it is sensitive to many internal and external factors. This limits it’s correlation to any one single factor, like VO2 or power.

Power is exclusively a measurement of external work and doesn’t tell us how the body is producing that power. There are many helpful models that can estimate internal intensity from external workload (a distinction for another time), but I’ve written previously about some issues I have with over-extrapolating metabolic information from power.

I still believe RPE – relative perceived exertion – is a better metric for simple tracking of internal workload. Hard workouts should be hard, and easy workouts should be easy. Your brain knows how to take care of the details.

Jan 24, 2019 – UPDATE

I’ve been able to test the VO2 Master Pro wearable VO2 analyzer, a new portable VO2 mask. I’ve compared actual VO2 values on various workouts and will be writing up my results. The first few articles compare VO2 for continuous VO2max intervals and for the Hard-start 30/15s protocol recommended here.

June 26, 2018 – UPDATE

I’ve written an UPDATE to this post where I reconsider a few assumptions given below. One major change is that 90% HRmax seems to be a better target than 88% HRmax. This post has been updated to reflect the changes.


Optimizing VO2max Interval Prescription

I left my conceptual post on VO2max with a tease for some practical application of VO2max intervals. Here’s where I’ll discuss some of the workouts I’ve been doing and the research that led me to them.

First, recall my definitions for T90VO2max (just call it time >90%VO2max) and MAP (Max Aerobic Power).

T90VO2max is used to refer to the duration or time (T) spent at or above 90% VO2max, ie. duration at near-maximal rate of Oxygen consumption as measured in ml/kg/min via lab analysis.

MAP is maximal aerobic power, which I use to refer to the maximum power/workload, and therefore shortest duration that will elicit VO2max before anaerobic energy system becomes the limiting factor to fatigue (read the last post for details).

VO2 Severe Moderate3_INKED2

Recall also that it appears that adaptations to VO2max are elicited by maximizing time spent above >90% VO2max (Rønnestad & Hansen, 2013; Seiler, 2010; Thevenet et al, 2007; I could go on…) hence why I think duration >90%VO2max is a valuable parameter of aerobic/VO2max adaptations.

This is the value I’m trying to maximize for my VO2max workouts.

Thevenet et al, 2007


Intermittent Short Intervals

It has been shown that intermittent exercise can elicit greater total exercise duration at high intensities (Rønnestad & Hansen, 2013Rønnestad & Hansen, 2015Thevenet et al, 2007).

Conceptually this makes sense: having brief rest intervals should allow you to maintain the target workload for a longer cumulative duration than continuous exercise. This is basically just restating the concept of interval training.

The 2013 Rønnestad & Hansen study referred to above found that 30sec work intervals with 2:1 work:rest ratio (30/15s) seemed to be most effective ‘short interval duration’ to maximizing duration above >90% VO2max.

Ronnestad 30s v tmax_INKED
Rønnestad & Hansen, 2013

I wonder if 30sec as a familiar ’round’ number allowed the athlete to better pace their effort? Compared to an individualized percentage of Tmax that might give some random integer duration (30/15s sounds better than 33/17s).

They followed up this study in 2015 by comparing this 30/15 protocol with a standard 4x5min 2:1 work:rest protocol. They found the 30/15 protocol was more effective at improving VO2max and performance metrics after 10 weeks training.

Ronnestad SI v LI_INKED2
Rønnestad & Hansen, 2015


Training with the Rønnestad 30/15s Protocol

The exact protocol Rønnestad & Hansen used was 3 sets of 13x 30/15s, with 3min rest intervals between sets. They prescribed a workload target of >88% HRmax as a proxy for 90% VO2max (update: I now recommend just going with RPE: start at 9/10 effort and try to keep that relative effort just below the point of blowing up. Easy!). The instructions given to subjects was to “perform at their maximal sustainable work intensity, aiming to achieve the highest possible average power output”

Power was used only descriptively as an outcome measure of performance, rather than as a prescriptive target: therefore if average power was higher for workouts later in the training program, this would indicate that the subject had improved their performance.

One of my recent Rønnestad 30/15 workouts

I’ve used a modified Rønnestad 30/15 Protocol on and off for the past year. It’s always a super tough workout, and I usually run it with 5min recoveries between sets, rather than 3min. I’ve still had to drop work intervals from the later sets, had to turn down the resistance, or just completely failed a set plenty of times!

When I’ve done this workout on my Wahoo Kickr I’ve prioritized a power target in Erg mode and used HR as a descriptive measure of time >90%VO2max, aiming to maximize duration >88% HRmax as per Rønnestad & Hansen’s prescription (as above, I now recommend going on subjective effort. Just make it hard!).

Prescribing Intervals via HR RPE or Power

If my intervals are prescribed via target HR RPE of 9/10, I will naturally put out greater power at the beginning of the workout when the effort feels easier. As fatigue begins to accumulate, my power will end up decreasing through the workout in order to keep the relative effort at 9/10, or “not quite blowing up!”.

This naturally produces a Hard-Start interval, which I talk further about below.

If my intervals are prescribed via target Power (eg. work intervals at 400 W) I’m more likely to hold a constant power output through the workout, especially if I’m locked in to Erg mode. My HR and RPE will be slower to rise than it would in the RPE-prescribed workout, since even as I fatigue the power will remain constant and unrelenting. Or I might even fail the workout at the given power target if I fatigue too rapidly.


  • Faster rise in HR and power when fresh
  • Plateau of HR and gradual decrease in power as fatigue accumulates
  • Constant 8-9/10 effort through the full interval, eg. just under the verge of blowing up.


  • Steady power output through the entire interval
  • RPE starts lower when fresh, and drifts higher with fatigue
  • Slower primary rise in HR and drift through the interval
  • Higher HRpeak and potential inability to finish


Hard-Start Intervals

I was very satisfied following the Rønnestad 30/15 protocol as my go-to VO2max workout. I felt like I was able to reach a good balance of output workload (power) and input workload (HR) in order to maximize duration accumulated >90% VO2max.

Then I encountered some studies looking at Hard-Start intervals.

Recall above that when prescribing workouts via HR, power will naturally start higher and decrease through the workout as fatigue increases. The body becomes less efficient at producing power during a hard interval, so for the same perceived effort and HR, power output will decrease.

Hard-start intervals are where power is manually modulated to maintain VO2 above target as long as possible – ie. to maximize time >90VO2max. This is done with an initial extreme intensity workload to rapidly raise VO2 and HR, then reducing power to match rising fatigue and maintain an elevated VO2.

Billat et al, 2013 found that by carefully manipulating power workload in real-time responding to subjects’ measured VO2 (via gas exchange analysis), they could maintain >90%VO2max continuously in excess of 15 minutes!

One subject was able to last fully 26 minutes at >90% VO2max!!

Billat et al, 2013. Shows constant power interval (blue) where subject lasted ~8min >90% VO2max. Compared to what they call decreasing-power interval (gold) where the same subject lasted ~26min >90% VO2max

This is obviously very compelling. But it would be difficult to manually manipulate target power in real-time for my athletes, or myself outside of the lab environment. So I would need a more generalized prescriptive protocol to plug into a custom Erg mode workout to be able to follow at home.


Practical Prescription for Hard-Start Intervals

Another study, Lisbôa et al, 2015 looked at a similar Hard-start interval protocol. They used a standard method of starting the interval at the maximum workload to elicit VO2max; what they called Ihigh, and what I call MAP, and finishing the decreasing-power interval at 110% FTP.

The interval duration was determined individually as the longest duration @ MAP (what they called Tlow, and is often called Tmax… sorry for the acronym soup) This duration was then divided into 4 equal intervals of decreasing-power, from MAP to 110% FTP.

They found the sustainable duration above >90% VO2max was over 50% greater, and total O2 consumption was over 70% greater in these decreasing-power intervals compared to constant power intervals at MAP @ Tmax.

Lisbôa et al, 2015


Combining Intermittent Short Intervals and Hard-Start

My immediate interest after seeing these studies was to combine the two workout protocol to rapidly raise VO2 toward >90% VO2max (which can’t be measured at home… or can it?) and HR toward >90% HRmax 9/10 RPE (which can be measured at home), and to sustain that duration for as long as possible.

I would start with a longer hard-start interval at MAP (highest workload over the shortest duration that elicit VO2max) then drop into a decreasing-power 30/15 protocol, finishing around 110% FTP.

Hard-start 30/15 VO2max workout… it hurts so good!

My HR rapidly reached near-maximal and then plateaued as the power declined at roughly the same rate at which fatigue accumulated. This particular workout I pretty much nailed the balance and managed to accumulate >36min @ >88% HRmax! (update: the accumulated time was less at >90% HRmax, and literally the entire workout was at 9/10 RPE!)

I was using 88% HRmax as my target based on the Rønnestad & Hansen 2013 & 2015 studies, although I now believe a better target for most people is to simply use subjective sensations and target an RPE of ~9/10. The big assumption here is that this HR target correlates to 90% VO2max… an assumption that I’ve been able to test on similar workouts. (Update: I’ve recently been experimenting with new models using muscle oxygenation to monitor internal training load)

The good thing about using Erg mode in Zwift or TrainerRoad is that I can have my hand ‘on the trigger’ to turn up or down the resistance in real-time. If I saw my HR drifting away from my target, or if I felt like I was about to explode I would rapidly raise or drop the target power a few percentage, which would instantaneously adjust the resistance of my Wahoo Kickr and allow me to continue.

WKO4 chart showing time and work (kJ) spent in approximate VO2max (orange) and Threshold (yellow) zones for the same 30/15 VO2max workout as above. Note the decreasing power toward Threshold during later sets as fatigue accumulated. Despite lower power output, my HR remained above target.


Prescribing a Hard-Start 30/15s VO2max Workout for Yourself

First, the disclaimers. Ultimately, there are a lot of assumptions built into this VO2max training protocol. Since we are unable to easily measure actual VO2 at home or out on the road we need to use correlated metrics to estimate our VO2 at any given time.

Namely, HR and Power.

There is an interdependent relationship between HR, Power, and VO2 that I still don’t fully understand.. but they have to be in the right balance for optimal adaptations to occur.

I believe aiming to sustain a near-maximal effort (RPE 9/10) and modulating power output to make sure you don’t blow up, will elicit the greatest time spent near VO2max. And that accumulated duration near VO2max is a critical parameter for enhancing aerobic fitness and endurance performance.

Ideally before prescribing this workout for yourself you should have a good sense of your MAP (Max Aerobic Powerthe maximal power that will elicit VO2max) and the maximum duration at this workload (MAP @ Tmax), and of course your FTP. MAP can be estimated at home with a Ramp Test (such as TrainerRoad, Zwift, or many others) or in a lab-based VO2max or lactate test.

Unfortunately, there’s no easy way to prescribe this workout based on percentage of FTP, since everyone will have a different relationship between MAP and FTP (see the recent Fast Talk Podcast for a fantastic discussion on the hyperbolic “death of FTP”).


Trainer Workout

The workout protocol I’ve been using is 3 sets of 13x 30/15s, 5min RI between sets. This should accumulate around ~10min of work each set, for ~30min cumulative work duration.

To do this workout on a smart/Erg trainer, the first hard-start interval should be 1 minute @ MAP, before going into the 30/15s work:rest short duration for 12-15 work intervals. Power will then decline in regular steps every ~3-4 work intervals toward ~110% FTP by the end of each set.

Your target will be to maintain RPE at ~9/10. Start each set too hard and modulate power to keep yourself just under the edge of blowing up. The point of this workout is to accumulate the full duration, so you’re better served by dropping power and finishing the set, rather than reaching exhaustion too early.

The second and third sets can have shorter hard-start intervals, as HR will more easily rise toward your target due to accumulated fatigue, and spending too long at MAP will over-fatigue you for the remaining work intervals. I found average power for the later sets will inevitably be lower than the first set, but this is fine as long as RPE remains high.

If possible, have your hand near the trigger to adjust the power up or down as necessary in your workout app of choice, to avoid a death spiral.

Outside Workout

If you were to do this workout on the road the recommendation would still be simply go hard! Try to maintain a ‘near-maximal’ effort through all three sets, from start to finish. Modulating power to maintain the intensity without reaching exhaustion. Power will naturally decrease as fatigue accumulates, but the power of each 30sec microburst should remain well above FTP.

I haven’t actually tried this workout out on the road, so if anyone does.. tell me how it goes! And if you changed anything to make it easier/more realistic to complete.

20 thoughts on “Prescribing VO2max

  1. Whew, you are getting deep into it! I had the 3X30/15 interval marked as something I might try later on in my training (because you had mentioned it in an earlier post). I’m still building base right now, and am a few weeks out from these types of short intense intervals I think.

    I just started using TR, would this interval prescription be best utilized in what TR calls the Specialty phase? Close to or during race season? I’m working on longer more muscular endurance intervals now to raise FTP and would think these would greatly benefit me as my “other” HIT session during the week. Race on Tuesday, then these (or something like these) on Thursday. With everything else being mostly Z2/recovery and perhaps a junk/SS/sprint for the stop sign group ride on the weekend for a more polzarized-ish plan during outside season.


    1. Yeah, Cory like Christopher said below, I would intend this workout to be used as a high intensity VO2max workout, as part of a Polarized Physiological (Base) training. But it could also do a decent job reproducing the demands of crit racing, as part of Performance (Specialty) Training phase.

      So again, I would recommend doing this kind of workout instead of SST/Threshold for Base training to raise fitness & FTP, as long as you’re aiming for overall physiological improvements (improving VO2max & endurance) and not into Performance training where you’re building for a specific event.

      If you’re racing right now as well (which I’m super jealous about!..) I would recommend one race and one HIIT workout per week. See the last post talking about how more than 2 high intensity exercise bouts per week probably becomes counter-productive.


  2. Jem may have a better answer, but as long as you are currently getting adequate amounts of Zone 2 each week (approximately 80% if i understood his other posts correctly),why not add this workout now? If you can keep the correct ratio and not over fatigue then why not? Seems like this type of workout will help build both FTP and overall aerobic fitness but with the same or less resulting fatigue than another SST/Threshold session.

    Liked by 2 people

    1. Thanks Christopher, agree completely with your answer.

      If ~80% of your workouts per week are easy Aerobic/Zone 2, then I think this decreasing power 30/15s workout is a great choice for the 1-2 high intensity workouts per week as part of a Polarized Physiological training plan.


  3. Best blog about cycling out there. Really great stuff, appreciate you taking the time to write your thoughs out on all this stuff. Way different than most other training/cycling/blogs that I’ve come across!

    Thanks Jem and Chris for the replies on my stupid training questions.

    I’ll give these a go and see how it shakes out.


  4. I’ve been reading your blog for a while and I think it’s very interesting, thanks for all the time put in! Keep it up! I have a question though, not specifically related to this post: how do you make sure your TSS scores are comparable? You seem to do a lot of work on the trainer. I, for example, can’t really hit the same numbers inside as out. So I have trouble estimating the TSS and thus CTL/ATL/Fatique when combining trainer rides with ‘real’ rides. Is this something you take into account or don’t you use the CTL/ATL/Fatique stuff that much in your training plans?

    Liked by 1 person

    1. I haven’t talked a lot about planning training blocks by TSS, CTL, etc. but that is a part of my season-long planning. I set a target CTL & TSB for my A-races using the Annual Training Plan in TrainingPeaks, and it builds approximate training load targets for every week.

      I don’t really prescribe individual workouts by TSS though, especially right now in Physiological Training focus. I think the priority should be on hitting physiological targets (time at VO2max, power targets, etc.) and the TSS will follow. The rest of the week in a Polarized program is filled with Aerobic riding, either to a TSS goal or constrained by time.

      It should follow that if you only have (eg.) 6 hrs per week to train, your target CTL probably shouldn’t be 110, so weekly TSS will be related/dependent to training volume. Honestly, I haven’t paid any attention to TSS yet this season, but I’m accumulating what I need to just by following the Polarized plan with the time I have available (which is more than some, and less than others).

      re: hitting the same numbers on the trainer as outside, there’s different approaches. I haven’t experienced that issue so I can’t speak first hand, but some people will test to determine a ‘Trainer FTP’ and base their workout targets and training load on that, instead of your ‘Road FTP’. There’s pros and cons to that approach. Physiology and psychology are different on the trainer, so it should follow that FTP could be different as well, but you might not be doing yourself a favour by inflating your TSS by ‘underperforming’ your actual FTP on the trainer versus out on the road.

      TrainerRoad’s podcast ( has some great advice on how to handle different numbers outside and inside. I recommend digging through their archives to find that topic.


  5. Hey! Thanks for a good blog post. Very interesting. I’ve been following Stephen Seilers research and have been using a polarized training approach based on that. So far so good. Never been faster actually. The 30/15 approach is something I know Giant Alpecin and Trek Segafredo uses but they use it more for tapering before races with a decrease in volume. Source of this is Mattias Reck who has worked for both teams. Instead of doing a 4×4 with 4 min RBI they do 4×6 minutes with 40/20 on/off. FTP @ 125% during the 40 seconds and very easy during the 20s. They also do a similar one for 2×20 minutes but @ 110% of FTP. They only look at the power numbers though and are not interested in HR levels. He also mentioned that depending on physiology of the riders they have different approaches. Climbers and GC contenders for example seem to reap big benefits by doing sweet spot rides where as sprinters just get worse doing this. The saying they have for sprinters like Kittel and Degenkolp is that “it’s easy to fuck up a sprinter” so you don’t want to be putting these guys with on faster group rides as they just can’t handle the fatigue the same way. This probably has to do with different muscle fibers and such. Well, thought I’d drop a line about this. Interesting article and I will definately start switching out my 4×8+2 intervals @ 110% of FTP to these intermittent ones 🙂

    Liked by 1 person

    1. Oh cool! Thanks for that. Good to know how the Pros are using similar workouts!

      I’d be really curious how they prescribe targets (based on tested numbers? %FTP? RPE?) and how that might translate to us mere mortals. I’m not satisfied either with using only or primarily HR targets (as per some great feedback on the reddit /r/velo post I made the other week).

      Had a good chat with a training buddy the other day, we were again considering the central vs peripheral focus of a workout like this compared to a ‘traditional’ 3-5min steady VO2max interval. My feeling (totally unsubstantiated!) is that this kind of workout is more centrally challenging, as heart & lungs remain elevated, but the legs don’t burn the same way as with a constant power interval.

      So another super interesting question is how riders with different phenotypes – more ANaerobic sprinters/pursuiters vs more Aerobic climbers/TT’ers might respond (or not respond) to a workout like this vs the traditional steady intervals. And how knowing an athlete’s fiber type composition might inform individualized workout prescription.

      Another area where the research can find ‘averages’ but averages aren’t as helpful when you’re trying to get the best out of a single unique athlete.


  6. Sorry to keep bothering you with inane questions. In the POL model (three zone model) is Sweet Spot considered Zone 2? I see that Seiler and others mention in the research that sometimes its not all 80/20, but often can be 80/15/5. That 5% in the Zone 2 area could be Sweet Spot, correct?

    Or should that 5% really be focused on Threshold? I’m guessing we would use threshold closer towards our race season in order to hit that spot on your power so you’re used to working in that area?

    I’m referencing this paper here, with this question


    1. Yes, in the physiological 3-zone model SST and Threshold are in Zone 2. The 3 zones are commonly defined (as they are in that paper) as:

      Zone 1 Low: under Aerobic Threshold (AeT/LT1/2mmol lactate)
      Zone 2 Moderate: between Aerobic and ANaerobic Thresholds (AnT/LT2/MLSS/4mmol lactate)
      Zone 3 High: above ANaerobic Threshold (and below PPO/Pmax/PVO2max if a 4th zone is used)
      Zone 4 Severe is often considered: above PPO/PVO2max. The paper you referenced doesn’t use this Severe Zone 4, so Zone 3 is anything above ANaerobic Threshold.

      So SST & FTP would be near the top of Zone 2 into Zone 3.

      The ’80/20 rule’ is very much a simplification, and usually does not (and should not) refer to percentage by duration. It refers more generally to number of workouts per week, eg. 20% of your weekly workouts should be high intensity.

      Even in a perfect Polarized training plan there will be incidental accumulation of workload within Zone 2, so if a study is looking descriptively at a real-world athlete following a POL training program, they will likely demonstrate something closer to a 80/5/15 zone distribution. The philosophy behind POL is to minimize time within Zone 2.

      You sound keen on finding somewhere to add SST into your program. You should! Maybe replace a high intensity workout for a few weeks and see how your body responds. You’ll get faster following the program you want to follow, rather than the program that you have to force yourself to stick with. There are plenty of benefits to training SST. I’ve talked only a bit about the benefits because other resources like TrainerRoad and Velonews Fast Talk podcast have done such a good job expounding the potential benefits.


  7. Being able to sustain >90% VO2 max is very interesting! Since that’s possible, shouldn’t we target 95% of VO2 max instead of 90%?

    My understanding is that older athletes or those with a lower max HR may benefit from a higher target HR if it can be safely done.

    Let’s use an example. A 20 year old and a 40 year old have a max HR of 200 bpm and 180 bpm respectively. That means for the 20 year old, 90% of max HR is 180 bpm, and for the 40 year old, it’s 162 bpm. 162 bpm is only 81% of 200 bpm. Since max HR decreases with age because of its pacemaker cells, the heart must feel like it’s exercising at a tempo or threshold zone which disagrees with polarized training. Maybe


    1. Good question.

      I don’t know exactly how VO2 & HR kinetics change with age, so consider this a best guess:

      As you suggest the older athlete could be reaching 90% VO2max at (eg.) 95% of 180 bpm, while the younger athlete could reach 90% VO2max at 90% of 200 bpm. Or both athletes may reach 90% of their own respective VO2max at ~90% of their own respective HRmax… It’s impossible to say unless they have directly tested VO2 & HR! Once again, %HRmax is not a great estimate for %VO2max, regardless of age. So I really don’t know which case might be closer to the truth.

      In your example I would assume that both the 20-yr old and the 40-yr old athletes would reach VO2max at 200 bpm and 180 bpm, respectively. The question remains at what % of their own VO2max will offer optimal adaptive training load, balancing duration and intensity. %HRmax is a less precise target and adds the aforementioned uncertainty to the question.

      Most of the literature I’ve encountered suggests that longer durations at slightly lower %HRmax or %VO2max (ie. 90-92% rather than 95+%) is more effective. So taking two subjects of different ages without knowing any further context or history, my guess would be that both 20-yr old and 40-yr old athletes should still aim for the same relative intensity, ie >90% VO2max or >90% HRmax, for their own respective VO2max/HRmax.

      If we are talking about a 40-yr old athlete who used to be able to hit 200 bpm but hasn’t seen that for years, should they still aim for the same target HR they were able to hit when they were 20-yrs old? That doesn’t sound right to me. It sounds like an athlete keeping their FTP set to their best-ever 20min test from 4 years ago… that number just isn’t relevant to the athlete’s current fitness. Percentage of 200 bpm just isn’t a relevant target to this 40-yr old athlete, because their entire system is currently maxing out at 180 bpm.

      Hope that makes sense. Good topic to research and discuss further!

      Liked by 1 person

      1. We might be able to argue that at 95+%, it’s not as effective since it’s less sustainable, leading to a reduced training stimulus. There’s more training stimulus at 180 bpm for 15 minutes than at 200 bpm for 15 seconds.

        I think it means there’s less potential to improve when the max HR decreases. The good news is that some people have heart rates much higher than predicted by the 220 minus age formula. There are rowers who claimed to have heart rates well above 200 bpm!


  8. Hi, super interesting article.
    I’ve started training recently with power meter, so any new knowledge is good.
    You mentioned few times about a time ” >90% VO2 max” but what is VO2max? is it power or HR? and how to calculate it ?
    During vo2max intervals (3mins) I reach 91%HRm in last 30 seconds.
    I know my HRMax (reached on few occasions during a run or bike on a trainer, but interestingly, on the same bike, on a road/outside, i can’t reach more than 92%HRm), Garmin says my Threshold is at ~89%HRm.


    1. ok, after reading more, i see that 90%VO2Max is close to 90%HRm
      and it would be good to keep >88%HRm during VO2max intervals.
      Today I tried 30/15 with a bit of hard start (but my HR oscilated around 84-86%HRm), I was able to do 2 sets with 13-15 x 30s/15s (but with long – 8mins rest between sets :/ ) next time I’ll go harder (with harder hard-start)


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