Is variation within interval workouts the future?


I read somewhere that there is “accumulating evidence that traditional interval training sessions can be improved by strategically altering the intensity within each interval”.

Do you know about the research that claims this approach is superior? How does that approach work? And what do you think about it?

I’ve always understood that the best would be to target a specific energy system by consistently doing the high intensity bouts within a workout at the same intensity. I think I heard you guys say in the podcast that doing otherwise runs the risk of building too much fatigue by hitting various energy systems, without getting a proper stimulus in any of them. And making recovery harder, because all the energy systems require (repair) work. So, except for specificity purposes, mixing up didn’t seem a good idea? I would love to hear your thoughts.


Where did you read that?

A recent study by, i think, Ronnestad indicated that high intensity work bouts starting at high power, then dropping of to sustainable power, provide more time at VO2max. Maybe that is what you read about.

You cannot target a specific energy system without also using the ‘less power producing systems’.
The only system you can target without other is aerobic.

Have a look at this vide for more details:

I only read a reference to this article: High intensity intervals: variety is the spice of success!. I don’t have a subscription (and read another article before), so can’t read it. So I don’t know much about the research or the kind of training they are talking about. Could very well be what you are referring to. Would be interesting to find out more!

Figured I’d share the study. From recollection, they compared ‘standard’ constant workload intervals to hard-start/fast-start intervals and variable-power intervals matched for time and total work. Main outcome was more total time near VO2max with either variable or hard-start intervals compared to constant workload.

Forgive me for commenting without knowing the full context of the article, but in the context of HIIT / VO2max intervals in the Ronnestad study, the entire work duration was within the severe intensity domain, in all interval types. If the goal is to perform a HIIT-like or a ‘VO2max’ workout, the first priority should probably be that the work is performed within the intended intensity domain (above FTP/CP/MLSS/etc). Before any particular optimisations need to be made around power target, interval duration, or pacing strategy. But otherwise, it’s a big zone to play around within.

If the article you brought up is more broadly talking about varying intensity across domains in a single training session, like a fartlek or ‘kitchen sink’ workout. That seems completely valid as well. Just depends on what the intended outcome of the session is and how it fits into the overall training programme. Interested to hear other thoughts.

Varying intensity across domains is what i used last year with my ‘compressed polarized intensity distribution’ (COPID) training designs. It worked very good and reduced the boredom of LSD. Power output increased over 25% in 26 weeks, across most domains.

The summary of that is: slow days and fast days, where the slow days consist of sub 5 minutes sections at hr zones 1-3, and the fast days have have zone 2 and 4/5 sections.
The total time and duration of the ‘fastest zone for a day’ increased over time based on fitness.

Sounds interesting. How did you get to this approach?

So essentially, you did your low intensity rides in a protocol of HR zones 1-3. Did you do something like that with the high intensity workouts too, e.g. targeting different percentages of ftp (probably primarily threshold and VO2 max)? Or were those more like the standard workouts, e.g. 5x5, 3x8, etc, targeting one intensity?

How did you get to this approach?

Well, first of all I found zone 2 sessions very boring and desired something with more variation.
After reading a lot of research I realised a few things:
. Training volume is key → whatever you do, do volume
. Only 60% of 1RM is required to improve strength → you don’t need a long high-intensity bout to get that result. And a ‘long’ bout will lead to a lot of damage, resulting in longer recovery, resulting in less (quality) volume.
Summed up: i concluded you can do intervals every day and should limit the intensity in such a way that you can recover within 24 hours. “Little progress every day, is a lot of progress per week”.
There are two ways to limit the stress: keep the work bouts short, or keep the intensity moderate.
So my easy days where ‘short bouts of zone 3 on top of zone 2’, just to create variation within the aerobic domain. By accelerating from zone 2 tot 3, you get a bit a strength development which you won’t feel the next day.
The harder days where short bouts (<120 seconds) of zone 4 on top of zone 2.
The total time in zone 3 on the easy days was 20% of training time. Same thing for the hard days.
I found that these percentages allowed me to recover within one day. The percentage should be tailored to your own fitness.
There seemed to be no need to increase the percentage though, as the power output will increase over time for the same heart rate.

Did you do something like that with the high intensity workouts too

I tried it for 6 weeks, but it made the concept fail as i could not recover within 24 hours. You can’t skate well (technically) in zone 2 if you have DOMS.
Also, there seemed to be no need to hit zone 5. During testing my power output in zone 5 increased equally to my output in the other zones.