Heart Rate (HR) during VO2 Max Intervals

I did Bluebell yesterday. This is 3x6 1 minute VO2 intervals with 1 minute recoveries in-between. While the minute efforts felt tough on my legs it wasn’t hard and I could have comfortably done at least another set, and my breathing and HR never really elevated maxing at 149 over the whole workout which is ~78% of my max HR.

Given that my HR never got near VO2 max range (in fact is still just in z2 according to Joel Friel’s threshold calculated zones), do I need to consider increasing the % effort for VO2 workouts?

My FTP feels right having tested last week, and for longer threshold intervals it always feels like I’m clinging on at the end, but VO2 ones generally feel very doable.

Other info;

  • riding on aero bars on a TT bike (in case that makes any difference)
  • Max HR 190
  • Resting HR 54
  • FTP 217
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Bluebell, as I recall, is fairly merciful among VO2max work. While you could increase the target power, if you’re on any of the TR plans you’ll soon be into more taxing workouts with longer duration work intervals. If you feel this way after something like Matthes, or workouts with 2-3 minutes of work at a time, then perhaps adjust. But unless 1-minute efforts are particularly important to you I’d leave it be. You’ll hurt soon enough.


I totally agree with @pkwell and find that these 30/30 or 60/60 type workouts are relatively ‘easy’ for VO2max intervals.

I feel like I reach an equilibrium pretty quickly, with HR typically around 150 (max 180ish).

Completely different story with 3 minute intervals at that same target power though, even with 3 mins rest! HR will be 170 by the second minute.

I’m sure Chad could fill us in on the physiology here!

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Bluebell is (relatively) easy. Did Ansel Adams -2 earlier this week (6x4x50/50 @130%), and blew up on Matthes +1 (9x3min @115%). Even if your HR doesn’t go up that much, as long as you’re starting to breathe heavily you’re doing what’s needed - and the 2 and 3-minute intervals will change your view.

Try something like Spencer, Mills -4, Mills -5 and report back. The Mills variants I listed are 2on/2off while Spencer is a classic 6 x 3on/3off. Let us know if those get your HR up over 170 (90%HRMax) and for how many minutes of the total work :grin:


Thanks for the replies. I think was just the first time that I’d actually paid much attention to HR as usually happy to just get on and pedal at the prescribed watts and was surprised that it was so low for VO2 work. I’ve done similar short sharp VO2 intervals running and (obviously being a different kettle of fish) HR spikes in no time at all for those efforts.

I have Mills in my plan for next week, and Spencer -2 the following, so will see how I get on with those!

This is just my experience and I am no expert but i don’t particularly like to 60/60 interval prescription. I believe it takes approx 90 secs to reach VO2 so the 60/60 just seems like the interval is too short and the recovery too long to really be able to impact your vo2 system. However, i do like 30/30s, 40/20s, 15/15s as they allow enough recovery to be able to string a lot of intervals together but not enough to reduce you HR. i also cam across the following article and have been utilizing these hard start workouts. I am seeing a really nice benefit from them.

Not sure if this will share but this is a good example https://www.trainerroad.com/cycling/workouts/543048-smart-hard-starts-


Sounds like you’re after Rattlesnake.

VO2 kinetics. Yours is most likely slow; that is, your physiology takes longer to respond to/achieve VO2max HR etc.

Those short on/off interval sessions just won’t do it for you. I’m also of the slow responded variety and have historically used either the classic 3-4min 120% intervals or the ‘hard start’ intervals mentioned.

TR’s answer to the hard-start is Rattlesnake. I highly recommend trying this at least once, it’s pretty cool. :snake::+1:

You really have to nail that start for everything else to work. And if you find your HR still isn’t hitting the VO2 zone, eliminate the rest periods and do each interval as a solid block.

Good luck!

Thanks for linking my articles! Very relevant for trying to estimate VO2 from power & HR, and for intermittent (eg. 40/20s, 30/15s, TR Rattlesnake, etc.) vs continuous (eg. 4x5min) intervals.

The short of it is, it’s unreliable to estimate VO2 from power & HR alone. But generally I would suggest power needs to be well above FTP and HR needs to be somewhere near maximal to accumulate time near VO2max.

Hard-start intermittent intervals can get you near VO2max, but the continuous hard-start intervals like the custom workout you posted will get you there faster and keep you there longer. Continuous intervals feel harder, because they are harder!.. And probably more effective at spending time near VO2max.

    55:45 https://youtu.be/VKjbIfSiNCU?t=3344

In Rønnestad last talk he addressed fast start intervals and a variant with multiple “kicks”. Whats interesting is that time at or above 90% VO2max rise, but RPE drop !
Unfortunately this studies are not published yet and no HR data was presented. Today i played a little bit with the kicks. I would say at least the RPE wasn’t higher then with continuous power. HR differences are not so significant different, least not in a single workout


I made custom VO2 workouts: 3x6min and 4x8min continuous Rattlesnake.

Recommend if you need a positive mental (aka ego) boost when doing VO2max work. Longer than the classic continuous intervals but easier, in some ways. :+1:

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Oh very cool. Thanks for that link. I know what I’ll be watching tonight!

Definitely my theory for using hard-start decreasing power intermittent OR continuous intervals would be to try and maximize VO2 and minimize anaerobic contribution (minimize blood lactate). That should result in a lower session RPE and faster recovery between workouts. But I haven’t been able to formally test this yet. I’ll have to look into what Ronnestad is doing on that front.

My experience is that intermittent stuff like 30/15 and 40/20 or short stuff like 1min/1min are little to no bang for buck when it comes to VO2. Even Rattlesnake as it is did not get me into VO2. RPE and HR were both low. HR was less than 90% and stable after the first set. To be honest, I was surprised and disappointed in Rattlesnake. A continuous Rattlesnake would probably work since that would be a hard-start decreasing power continuous interval. I haven’t tried adding a hard start to my VO2 intervals. However, I am a big believer in the decreasing power continuous interval.

Long story short, continuous intervals provide the most bang for buck (i.e., minutes of VO2 per total work time).

@SpareCycles I wish you wrote/posted more often to your site. Wealth of great information!

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@SpareCycles I wish you wrote/posted more often to your site. Wealth of great information!

Hey, thanks! I do too mate, I do too :sweat_smile: I’ve been doing some extremely cool experimentation recently, so hopefully expect some more content soon?

re: Rattlesnake with low HR & RPE. Have you tried just going on RPE and taking the smart trainer off Erg mode? You might simply have a higher work capacity above FTP, meaning you need to go harder to reach VO2max.

Again I have a problem with using the same %FTP for everyone doing VO2max efforts. Or any efforts >100% FTP really. The shape of your individual power-duration curve will determine what power and what %FTP you can sustain for high intensity intervals.

Everyone will respond differently to hard-start and intermittent or continuous intervals. Like @Captain_Doughnutman said it depends partially on VO2 kinetics, or how quickly your aerobic system responds to power demand. You’ll get much more benefit from finding your own prescription of intensity & duration that achieves and sustains VO2max.

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… as Seiler recommends.

Here the individual responses to long and short intervals from a experiment conducted by the university of Kent. Is a copeid from the excellent talk from James Hopker.

Regarding V02max we see at group level a better response to short intervals: But we also see one subject with a decline in V02max,
The presented experiment itself is very interesting. The better adaptions induced my the short intervals happened, even if time > 90% V02max was much lower. The researcher themselves was surprised about what the found. The speculate that time at or near V02max in only one driver to chronic adaptions.


Love your articles and have used the advice in my training. I use Xert to create the hard start intervals and they work like a dream! The smart intervals work really well. Keep up the good work.

20 minutes at VO2max. SUPER fun! I’m not sure it’s even ethical to subject participants to that. :wink: Way to go, Billat.


Seconded on this point. I did a couple of sets outdoors on my last cycling holiday / camp, went on power for the first hard minute to make sure I was on target, and then just went hard for 30 and easy for 15 over and over again, keeping an eye on heart rate only to try to get it above 90% for a decent period.

The power wasn’t quite the neat decline you’d get on the trainer, but it certainly felt like a good workout.

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