That’s simply not enough rest for me so I did 4 minutes of recovery. You want to be able to complete these intervals, resting for a mere 2-min doesn’t allow me to do that. You could certainly experiment though…
FWIW, I also do a 30-second hard start on these to get HR elevated quickly.
I have done a lot of intervals with a 2 minute rest over the last couple of years, but recently introduced 4x8 to my repertoire. It’s not easy and when I have done the majority of them out of racing season my FTP has not been stable so it is hard to put a figure on the intensity. But I have got good at pushing myself to get through the later intervals. In my last 4x8 my heart rate at the start of the interval increased from 119 for the first to 132 for the last. At the end it was 152 for the first and 172 for the last. I was able to increase my power on each interval too. I think I could have probably increased the intensity of the first interval, but was really pleased with it as a workout.
The 8-minuter’s are interesting and require more experimentation with regard to power output and modulation. If I do them indoors I’ll do the main interval at 105% of FTP and go from there. When I was doing them I found that it usually took around 90 seconds to hit 90% of HRmax.
The hard start really helps get that heart rate up quicker so you spend more time in that 90% or higher range.
Ive started doing 8 min intervals recently on a polarised model, using long rest periods still (about 1:1 work to rest), gradually trying to reduce them though
I average about 90% max HR for the 8 mins, takes me about 2mins to reach it using a steady power for the interval
So far i am feeling improvements, and holding a bit more power for my 8 mins. Ramp test at the end of this 4 week block will tell me for sure. This is the 2nd 4 week block of trying out polarised for me, lots of zone 2 which im enjoying, gives me good opportunity to work on my TT position on the road
Phil - thanks for sharing your experience with these.
I find it particularly interesting for a few reasons:
dogma says we should mix it up with workouts to keep adaptions coming. Just progressing the same session for that period of time would usually be frowned upon by many, but it clearly shows your progression of reps and intensity was enough to keep you improving
your age - I’m 51 this year and seem to have struggled to see ftp increases with SST & threshold work, so maybe getting stuck in at 90% HR max is what might help?
your 10hr training week, which I guess gives you about 8hrs z1 time and 2x1hr of 30/15s…not huge volume or TSS I guess but again, still driving improvements
the 1 or 2 x 30/15 session per week question - I had settled on a 3 sessions in 2 weeks plan in my mind, but with a little more overall training load of probably around 15hrs per week. I’m not sure I could complete 2 quality interval sessions without reducing the z1 intensity even further, so aiming for 1.5 sessions per week seemed sensible, and your example makes me think it would potentially work.
I know we’re all unique so YMMV, but this is great input so thanks. Look forward to hearing how you get on with the 8 min intervals.
I did a ramp test yesterday and the once a week 30/15 (in addition to the Z1) has maintained my FTP / VO2 max power since last July.
So I think your doing 1 session one week, then maybe do 2 the following week is sound. I like that I’ve been able to keep it going all year without any burnout or mental fatigue.
Don’t be afraid to miss the second session or delay it 24 hours if you’re no feeling. Sometimes I’d get into the first set of intervals, realised it wouldn’t be quality. So binned it and tried again either later that day if I was attempting a morning session, or the next day if attempting an evening session. Most times just waiting a few hours made all the difference.
I’ll be kicking off the 8 min intervals on Monday. No idea what power I’ll be able to do. So I’ll probably just try one 8 min interval not in ERG mode to calibrate what the pacing feels like. Then I’ll dial that down and try 2 x 8 min following week etc.
Likely do it once a week for first 3 week block initially. See if that on its own brings improvements. No point doing more intensity than necessary. Then if that plateaus look at adding a second session a week.
My 30/15 sessions have 15 min warm up and cool down periods. Initially I had a 5 min warm up and it does make the average power look better. But I find I can better manage the intensity if I’ve had a longer warm up. You obviously want to bring that HR back down before you try climbing off the turbo. You may find your legs a bit wobbly when you climb off!
The total of the two 30/15 sessions if doing 13 intervals comes to 2 x 3 x 13 x .75. So 57 minutes a week of actual intensity. Plus additional hour of warm ups / cool downs. I found that more than enough at my age 
Thanks for the follow up and additional detail. Its all very helpful and again, very impressive & interesting that the same session continued to maintain your FTP/vo2 over winter. FWIW, I started a block of extending tempo, then SST work in Oct through to Xmas, and it certainly helped my TTE but I’m not sure I got a significant change in FTP over that time. That was based on at least 3 sessions a week as well, so your single 30/15 session probably did the same in much less than a third of the time 
I’ve never done much dedicated vo2 work as I just wimped out when it came to the RPE involved. I would happily do SST/THR for hours on end as it suited me, but I need to change that. The last 4 weeks I’ve really started to work on vo2 intervals and tried lots of different forms on for size - so far 40/20’s feel like the one, although I havent done 30/15s yet. I do them on the rollers which requires clicking up and down about 6 gears between work and rest, so 15 secs just feels like it might not work so well just from a practical standpoint. I’m still dialling in the intensity and learning how to moderate it to get my HR >90% and keep it there without blowing up but its coming together and I can already feel that I’m handling the RPE better and pushing myself harder right to the end. Your example has inspired me to aim for consistency and keep going with these while building the work time each week. I just need to build the work time now beyond the 4 x 6x 40/20 I completed yesterday. I guess this gives me lots of room for progression!
FYI, I watched these tonight and found them useful - Seiler 3 parter on short-interval stacks. It may not be new to you but there were a couple of his review slides in there where he commented the 8 mins of short intervals were effectively/metabolically the same as an 8 min continuous interval. Makes me wonder is 4 x 8 is really different in effect than 4 x 12 x40/20???
Yes I think my HR trace is in my post up thread. I found my HR dropped 1-2 beats in the 15 second recovery interval. It really does stay high. When I used to do 30/30 my HR just dropped too much.
I am intrigued to see how my HR trace looks for the 8 min intervals. I used to shift gears as well. Though I use bar ends on friction , so jumping 6 gears is one smooth action. What I’d generally do is once the countdown timer got to 3 seconds to an on interval. I’d shift the gears and up the cadence. That stopped the trainer getting bogged down with excessive resistance.
During the on intervals initially I couldn’t look at the countdown , even 10 seconds to go seemed an eternity. So I’d just put head down and keep the legs turning till it eased an I knew I was in my 15 second rest interval. As I got the measure of the rpe I was able to look at the timers counting away and just accept it was hard 
Going back to your manta on dogma about different workouts. That used to be me. Had all these different workouts schedule. Different intensities / different durations, different rest.
The problem I found was that if I delayed a session because I wasn’t rested enough. Then it got mentally taxing remembering which workout I meant to be doing as I shuffled things around.
So I settled on the 30/15 and if it got moved I no longer had to workout what I was doing next. If it’s a hard day then 30/15s it is!
So I like to keep it simple and because I only do them once or twice a week I don’t find it gets stale at all. Doing the same workout but maybe more intervals per set. You also get a sense of whether you are improving. You don’t need to wait for retest to get a feeling on it,
when people talk 4/2 or 8/2, I’m assuming this means 4 or 8 min of work, 2min rest?
Seiler’s 4x8/(2 min rest) prescription say nothing about heartrate. The goal is to produce the maximum average power over all intervals. The heart rates and power are not prescribed, and (from memory, and from my results) HR ends up around 90% HR max, and the average power comes to around 105% of FTP. At the end of the first interval HR is around 85% HR max. So when I do this workout, I aim for 105% ftp, and if I manage all intervals at this power, I increase it by 5-10 watts.
If anyones interested, i made these workouts:
13x 13x30/15
4x8
6x4
You need to share them in a team, then have people join the team so they can acces the custom workouts
in all his videos and interviews he’s always referencing the time spent >90% HR max. Its worth a watch of the 3 Seiler YT videos linked above that reference what he calls the ‘short-stacked’ intervals eg 30/15, 40/20 etc as he discusses these in relation to longer intervals like th e8 mins and the importance of HR.
He’s pretty clear that if you aren’t getting >90% HR max then its a threshold session…
I like that thinking, especially as I’m very prone to over thinking all this and making it too complex. Problem then is I jump to another approach and probably dont see things through for long enough to get the real benefits!
I just had my first A event bumped back 8 weeks to late June, so now have 16 weeks before any events. I’ve made the firm commitment to a polarised approach and will continue to log as many z1 hours as I can, but you’ve pushed me to commit to 8 weeks of 40/20s and track the improvement with that. I like the simple approach - easy days EASY and hard days 40/20s!
Just rewatched the 3rd part.
Did you also note bit he said about pgc alpha-1 one? That protein is associated with mitochondrial biogenesis. He referenced a study that took muscle biopsies. Basically the hard but not super hard interval sessions significantly up regulated this protein in the muscles.
So I think he’s come to the conclusion of >90% HR max as his sweet spot but don’t push the HR too far beyond there. The ideal effort to produce that up regulation and adaption.
I’ll be interested in my HR response for 8 mins intervals. Then it’ll be a case of which ones I prefer , the 8 mins ones or 30/15? It may even be a case of switching between them if I like them equally. But I’ll probably do three week blocks of one or the other. Keeping it simple.
Like is a funny word isn’t it, when you are doing something you know will be hard. But after a few times doing them you do get in the right mental zone for them.
That was the part of the 3 videos that I found hardest to understand based on his descriptions, except I got the same takeaway - too hard is actually going going to be less effective.
Look forward to hearing how you get on, although there will obviously be a learning curve for you to get as comfortable with the 8 mins as you obviously are with the 30/15s.
I’m going to stick with the 40/20s for a while, but first I need to get more disciplined with my z1s…last 2 days I went too hard rushing home and accepting a ride with a mate who wouldnt do z2 
Now time to return to quality solo time.
Edit: Just listened to an old Fast Talk podcast episode 3, which referenced a Seiler study about reversed periodisation. Key result was that groups that consistently did the same intervals over a period of weeks did much better than the group that mixed up different length intervals during a block eg 4/8/16 min intervals. The order they did blocks of those 4/8/16 min intervals made little difference - so consistency really is key.
As part of my plan, I’ve now done two 4x8 (2m rest) Seiler workouts.
First was at 106% (286W target), and I found it perfectly manageable. I hit 90% to 93% max HR over the 4 intervals, and averaged 286W, 286W, 287W, 289W. I felt great that day, hit the targets, and didn’t think it was too bad.
Second was last week at 111% (300W target), which was too much. I hit 301W for first interval and 93% max HR. I hit 94% max HR and had to quit 6 minutes into the second interval. There was no recovery from there. It wasn’t my day, and I didn’t feel 100%, but even on my best day I’m not sure I would have hit the target for all 4 intervals. I’m repeating it next week, and I’m guessing my coach will set it somewhere between 286W and 300W. I’ll report back!
Up to now, I’ve gone through a base period of absolutely no VO2 or any kind of intensity from Oct until end of Dec. I’ve had more intensity and VO2 work added to my plan as of Jan, so still sharpening and improving there.
So between a 1-2 BPM increase in max HR per interval?
