Seiler’s 8-minute intervals (Polarized)

today i did 6x8 min with 105% MMP60, based on my test one month ago. Probably me FTP now a little bit higher- 90% HRmax I reach at the end of the second interval, after 4 min of the third, and for last 3 intervals more or less after one minute.
I made it more to work closer on race pace and calibrate my feeling.
The RPE is nor harder then 4x8 with 2-3% more. But witch one will be more effective ? I have no idea

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I recently did a quick and dirty respiratory rate test and plotted it on excel. I usually breath in 5 pedal strokes for most of my endurance pacing (or 5 steps running). Since I’m usually at 90 rpm on the bike and about 180 steps running, this is about 18 breaths/min and is pretty consistent from about 180 watts up to 225-230. At 240 watts, my breathing increased to about 21-22 breaths/min and HR averaged about 76-77% of max for the two later segments. Supposedly the actual lactate turnpoint is still a bit higher than this, but not really sure without doing some real testing. Seiler uses the 75% cap as that is a ballpark average and good starting point, but the actual physiological change is going to be very individual.

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Another go. This time I set the intervals at 103% and adjusted up or down (mostly down) to hit HR targets of 89, 91, 93, and 95% of HRmax at the end of each interval.

Good news - I hit heart rate targets perfectly, and got a record 20min high HR for 2019 without killing myself.
Bad news - my power was low, especially considering the numbers I was hitting in my race on Sunday. This might have been down to fatigue from the race, the fact I did the workout early morning with hurried fuelling, or possibly the heat (temperature of room was 17-19 C despite 1 fan and an air mover pointed at me).

Question I’m asking now is, if I hit my HR targets but wasn’t hitting power, was I getting the full adaptive benefit?

I would say yes, because HR is a good indicator for VO2. If HR tends towards it’s max, VO2 do so

Today 6x8 with 106%( based on MMP60 one month) ago. I hit the 90% in the second interval and end up with 94%. The session gave me 30 min >= 90%.
I think very nice HR.kinetics

Now I’m very happy to perform LIT sessions :wink:


Great work! I did the 4x8 again last night. Amazing the difference doing it in the evening and fuelling properly makes…

Wednesday: HR 153 avg across work intervals, power 276
Yesterday: HR 150, power 282

I think my HR was a bit lower because I paced the final interval too conservatively and need to ramp the power up a lot in the last couple of minutes to get HR up to 95%. But overall, I feel I’m pretty much nailing the session as it’s intended. Now for a 5 hour ride at <70% maxHR…


As the original poster I thought I should update some things:

I have now done the 8*4, on 3 separate occasions. Each time, floating between 105-110% FTP.

I have also found it’s quite easy to achieve if you precede it 4-7 prior with 6 minute intervals at +2% of your target intensity.

So for example
Week 1: 5x 6@108% / 4x8@105%
Week 2: 5x 6@110% / 4x8@108%
And so on.
The alternate days, I have been making up with Baxter - 2 / zone 2 road riding (with the occasional V02 reps on the 20% hill near my house)

I have also noted my HR sits around 90% during the 8 minute intervals, fine by me, any higher would be silly.

The biggest caveat I have to give is these are fatiguing, I have found the 8 minute intervals, while not creating localised muscle pain, leave me in a fatigued state for at LEAST 72 hours. Therefore; in terms of building intensity, Ill be discontinuing this cycle after my next race (12 days out).

Saying all that, I ‘feel’ like my FTP is increasing (probably due to RPE dropping on 8min efforts) and will re-calibrate that metric after my next race.

I would disagree with Thorsten and say that HR can be adversely affected by other factors, including stress, lack of sleep, etc… and you may not actually be achieving >90% of VO2 max, which HR bpm is a proxy for. You could try giving yourself an extra day’s rest (or easy ride) before attempting the interval day. You really want to be able to hit the power goals for the intervals, which will hopefully trigger the desired level of oxygen uptake response.

I have very low HR kinetics during these long intervals and cannot achieve >30 min of HR 90+ max, so I am going to add “hard starts” to the beginning of my intervals to drive my heart rate up. Jem Arnold’s Spare Cycles blog ( talks about these, as does a recent presentation by Ronstadt ( at min 56:06).

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Yes, there’s been a bit of discussion of hard start intervals over on this thread.

As it happens this Tuesday I was planning a 4x8 on the turbo, but when I got home, the room felt really humid and I realised I’d left my earphones at work. Disaster!

So instead I went outside and did hill repeats, roughly a 7x3 vo2 session. I did a hard start on each rep to try to get my heart rate up, and then went on feel and heart rate for the rest of the interval. I ended up with a lot less total time at 90%+ maxHR than on a 4x8 session, but it felt good and hard nonetheless. And if I had stayed indoors, I’d have probably thrown in the towel after 2 intervals…


Inside a HIIT block my HR drop. Training overload affect the HR in my case. But I can hit my power goals, indeed i can even rise power slowly inside this block. What i see is dramatically rise in the efficiency factor. I speculate that in case of functional overreaching the HR maybe isn’t a good indicator of V02 uptake. Some hint are also in the first talk.

I’m not sure witch statement you mean ? For me HR is not significantly affected my stress, lack or of sleep. Even heat affected the HR with long delay. But I don’t generalize this for other subjects.

Good observations.
I was looking for information on this kind of intervals and came across with your reply.

Today my coach prescribed the following workout:

2 blocs of 6 intervals of 4min @105%FTP w/2min recovery between intervals and 5min recovery between block 1 and 2 (i.e. between rep 6 & 7). My RPE beforehand is… “I can’t do this”.
What are your thoughts? 48 min @105%FTP in a session seems a lot to me (but not to my coach).

Which as a TTer is just want you want. Maybe not for crit races though

How did you do on your two sets of 6 x 4?

I’ve had many workouts where I didn’t believe I could do it. Then did. Its a good feeling when that happens.

Sometimes a coach will give a big test to see how the athlete does both physically and mentally.

I did Jepson recently which is 4x8 min. with 3 sprints inside each interval. The rest period was 4min. between sets. For some reason I decided to do this workout very hard once I got going:

1st 312w 104%
2nd 319w 106%
3rd 319w 106%
4th 324w 108%

I’m sure this would have been much harder using the Seiler 2min. rest instead of the 4min., but I’m pretty sure I would be able to do 105% for each.

I was doing a fair amount of 4 x 8 last year, if you’re jumping in at what amounts to 12 x 8 I’d say that’s going to be very tough. Seiler himself says that stretching the 4 x 8 out to 6 x 8 is a tough session. I’d never attempt 2 x (6x4) tbh.

My 25 mile TT races have given me a hour FTP very similar to my measured FTP (using the 20 minute test).
I am not sure I could replicate that on a turbo because the natural tendancy is to hold back a little whereas in a race I will just keep on pushing at what I think is a power I can maintain (judged by feel rather than watts)

Thanks for your interest! The same thing happened to me. It went surprisingly well.

Nailed the workout but struggled with high cadence on the last couple of intervals.
The other key session mid week was harder to me: 2 sets of 6x2min @115-130%FTP w/ 1 min recovery. HARD AF. As you can guess, first two intervales leaned towards the side of 130%FTP, which resulted in longer recovery periods for the last intervals (backpedaling, what stops zwift / TR) and not nailing the workout.

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Sure, recovery time is the key part in this kind of workouts. Those extra minutes help a lot.

Seiler references a few studies that show that the benefit in recovery between two minutes and four minutes was actually not that great, which is why he went with the 2 minute recommendation.