Low HR in VO2 Efforts during polarized training

TL;DR tempo HR in 8x4 sessions, huh??

I’ve been doing sets of 4x8min at 103-105%FTP and 30/15s at 120-130%FTP. These have been done on both the road and trainer, but my HR as a percentage of both max and FTP is low.

Although it’s been a few years since I’ve trained seriously this years numbers are consistent with what I’ve seen before a max HR of 201 and threshold of 181 with a resting of ~50. These numbers were taken from test on the trainer this year - but I see similar during races and during outdoor tests in the past.

VO2 zone is either 190+ with the 7 level model, or 177+ for the 3 level model from Seiler. During a recent set of 4x8 (outside) HR average for all for intervals was 162-169bpm maxing out at 177 during the last minute of the last interval. This seems inconsistent with the proscribed HR guidelines for the session, and that I’m on my knees for the final minute. Though 30/15s I feel that 130% FTP is within my capabilities. Doing these on the trainer - I do have a higher HR, but not massively so - I’ve put this down to cooling and other issues with riding indoors.

So - carry on with intervals as they are? Or use hard starts to get the HR up during the 8 minute intervals, if so how hard for how long?


Carry on. Don’t worry overly about HR, it’s a useful metric to keep an eye on but it varies quite a bit with temperature, caffeine, freshness, fatigue, etc. Not to mention the huge variance from one individual to another.

If you’re newly returned to serious training then this may just be your new normal for whatever reason. Could also be that over time your HR will gradually go back to what you were used to from previous training. E.g. Maybe right now your muscular endurance is more of a limiter than your aerobic fitness, so your legs are at their limit while your HR still has a bit more to give. In which case maybe as your muscles get stronger and demand more oxygen you’ll see higher HR during VO2 intervals.


Is your FTP too low?

So you’re doing 4 x 8 minute efforts at a little over FTP, and your HR is hitting 81-88% of max? That’s about right, isn’t it?

Here’s my logic: 81-88% of max HR would be about 80% of VO2max, which makes your FTP about 75% of VO2max - which is within the normal range.

Increase the difficulty by increasing the % of your ftp. The hard stuff in polarized training are supposed to be difficult. Vo2 intensity isn’t exactly a heart rate zone.

I have the same MHR (slightly lower threshold) and my numbers are similar for a 4 x 8 session. I wouldn’t sweat it if you’re seeing improvements :slight_smile:

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Thanks for the replies… seems like I’ll just carry on as is and wait to either get better or give in to ageing.

my understanding is that VO2 is more about stressing the cardio vascular system, then say long Z2 - which is energy and cellular developments. In the Seiler & Rønnestad stuff that I’ve read they seem to place some importance of time in zone - based on HR. I don’t know if I’m reading it incorrectly or they count intervals time as time in zone (which makes sense).

Probably not - did both a classic FTP 20 minute test and a CP3 max effort before the start of this block and both were in agreement that I’m unfit.

Ok… when you put it like that seems to make sense.

This does seem to make sense, as I’ve gone for VO2 first then base, as I’d like to feel fitter, before getting fitter.

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I know that feeling well! It’s the cycling equivalent of “fake it until you make it”.

If this is the case then I’d stick to the short interval sessions for now (Baird, Rattlesnake, more 30/15s, etc). Then return to the Seiler intervals after base.

Basically if you don’t have the muscular endurance to push that much power for that long then you’re never going to reach vo2 max. So the session will just be in a kind of no man’s land, intervals not long enough to really improve endurance, but not high intensity enough for vo2 max.

For me to hit low to mid 90% of HR max with 4x8’s I have to do them at 110% of FTP at a minimum. Otherwise, I’m hovering slightly above my LTHR. I also don’t see as high of HR when doing 30/15’s or other short/short VO2 max intervals.

I see the best response when doing 3-5 minute efforts at no less than 120% of FTP. For me those are bread and butter VO2 interval durations.


Interesting. I’m probably going to ignore your advice and finish off the final 2 weeks of the block, but I think it’s good advice. I might play about with interval intensity / duration like @anthonylane and @codybraithwaite7 have suggested as it’s 2 weeks I have to mess about before I have to think about knuckling down and building out a base program. I’m also tempted to stick a taper and peak week onto the end of it just to remind myself what they look like.

Actually, long Z2 rides can stimulate VO2.

Going back to 4x8. My take on them is that in order for me to get into VO2 max I have to hit them at a high percentage of FTP and they are long. I’d rather put myself in the box more times at 3, 4, 5 minute intervals than fewer, but longer. If that makes sense. I think this is why people find 30/15’s and 40/20’s to be even easier, mentally. While the rest intervals are hardly rest, the work intervals are so short. You just bang em out.

An 8-min a VO2 max interval, if that’s even possible (I don’t think anyone, but a few, can truly do 8-min @ VO2 max) is an eternity. 3-min is more (still hurts like a MF’er) palatable.

Regarding your HR, are you positive you’re not in a fatigued state? I’ve had workouts where my HR response was unusually slow, and I never get the numbers I normally do. I chalk that up to a bad workout probably due to fatigue.

My numbers are similar to yours as far as heart rate. And I can relate to seeing the heart rate stay a tad bit lower than I want if I’m doing 5 to 8 min intervals at about 105%. But I see this usually on the first and maybe the second interval, but any intervals after the 2nd one, my HR will climb a bit faster.

Like you mentioned, a hard start should absolutely bring it up a bit quicker. Then you’ll just have to see if you have the legs yet to keep it going once you settle in. Id recommend hard start at about 50 to 75 watts higher than your settled in pace and try it for 30 seconds and if it sort of works but you want more go for the first minute elevated.

And then the next option which has been stated is to do these at 120% and above and see if you can even get 2 minutes in. Or… do your first interval at 120%-plus, for say 2 minutes, then rest and bring the next intervals back down to your 105 to 110 % range on the 5 to 8 minute lengths.

And yes, all of this could be related to not having an ( accurately set FTP number ) but lets assume it’s close.

Your heart rate data is similar to mine. 204 max, 181 threshold, resting around 48.

For VO2 work like what you’ve described, with a typically short TR warm up I would not hit 180+ until the 3rd interval but it always gets into the 180-185 range before the end of the workout.

When my HR is lower and I’m completing the workout without issue and the RPE is inline… it’s ramp test time.

Fatigue is probably playing a part at the moment - coming into the final (2on 1off x 3) block. Though I’m finding it hard to quantify, I both feel like I’m pinging and popping at the same time - I’m putting it down to not having much endurance to soak up the intervals, and structure rather then panic training.

Even if it hasn’t had a huge impact on my FTP, my 5minute power (and I’m hoping 1minute too) is going to be much better when I get around to testing in a few weeks. These are key numbers for me to work on so it’s good to know it can be done in 9 weeks from key events.

And the winner was… @HLaB.

Life conspired against me so 3hours on the road wasn’t an option. I decided to do an FTP instead. +30W. Just shy of 12% improvement in 6 weeks. A much larger jump than expected, but I’m not complaining.

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