Comparing Steady Power to Decreasing Power

Just a cool comparison from my workout yesterday, that offers a chance to compare steady-power 30/15s intervals to decreasing-power 30/15s intervals.

I set out to do 3x sets of my favourite VO2max workout, because with the vascular issue in my leg I’m scared of I can’t do more effective continuous power workouts. I wasn’t sure what my power target should be, since I haven’t done any proper VO2max intervals for a few months. So I set targets conservatively based on my current power-duration curve.

The workout targets were supposed to look like:

3×13 hard-start decreasing-power 30/15s… turned out to be waaay too easy.

Immediately I could tell the power targets were too low, so as the intervals progressed I kept turning up the resistance to keep it hard. This unintentionally resulted in a fairly steady ~390-400 W power output for Set #1.


Let’s compare Set #1 to Set #2, where I started with the resistance ~10% higher and allowed the power to decrease through the set. The first hard-start interval was at ~425 W and the final interval was ~380 W.

Colours are automatic.. don’t blame me if they clash!

So what are we looking at?

  • First thing to notice are the power bars. Orange in the top chart (Set #1) and Yellow in the bottom (Set #2). This is raw second-by-second power.
  • In front of the power bars is a smoothed area of ‘MAP power’. Blue in Set #1, Purple in Set #2. This is a formula meant to estimate work done above 90% VO2max, using WKO4’s model for VO2max based on the power-duration curve.

ok, quick sidebar on ‘work’ and ‘workload’:

What are ‘work’ and ‘workload’?

Work, in joules is the product of power (watts) multiplied by the time (seconds) that power was held.

Work (J) = Power (w ) * Time (s)

Workload, in kilojoules is then simply the cumulative work done for the given interval.

Workload (kJ) = sum( Power (w ) * Time (s) ) / 1000

VO2max workload represents the ‘raw’ power done through each set within the typical VO2max training zone, and is represented by the predominant orange and yellow power bars in the top and bottom charts, respectively

MAP workload estimates the work done above 90% VO2max, which is really the number that counts for a VO2max workout. Blue in the top chart, purple in the bottom.

The MAP expression tries to account for the slower ramp-up time of VO2 when each VO2max interval is initiated, so you can see by the coverage of each area over the power bars that not all of the VO2max workload is contributing to the MAP workload. The first part of each work interval is spent just ramping VO2 back up to 90%, before work can be accumulated above this target.

This is why the comparison between sets is so interesting!

Compare Workloads for each set:

VO2max Workload
Set #1: 159 kJ
Set #2: 167 kJ

MAP Workload
Set #1: 57 kJ
Set #2: 101 kJ

While both VO2max workloads are within 5%, MAP workload shows a massive ~43% difference!

Normalized power was also higher in the second set (330 W vs 350 W) so maybe the improved quality of the second set is no big mystery, but I find the difference in MAP vs VO2max workloads the most interesting takeaway from this workout. This also suggests that NP is a better estimate of training workload than Avg power (which we kinda already know!)

Using intermittent intervals like the 30/15s and knowing the MAP formula, I could probably design a workout that would game it to maximize MAP workload, but the formula is just an approximation.

As a model, it’s sure to be wrong… but it is useful.

I’ll leave this with a sneak peak of a chart I’ve been working on that attempts to model VO2max training load using the MAP workload algorithm. It then tracks it in a PMC-like chart with Chronic and Acute training loads.


11 thoughts on “Comparing Steady Power to Decreasing Power

  1. I’ve been loving these decreasing power intervals and feel they rapidly lead to a (positive) adaptation in perceived effort and sustainted power. I’d love to have you input on hhow to extract the best from them if you can. Best!


    1. Hey Frederico, thanks!

      I think the 30/15 workout is great, and I’m starting to do some testing looking at how my own VO2 responds to the intermittent protocol. The initial numbers (on Strava: look very compelling. I’ve been thinking more recently how intermitent protocol like this interact with peripheral energy production, eg. myoglobin desaturation & resaturation and PCr/glycolytic contribution at initiation of each microinterval. I don’t know enough about those mechanisms to draw any conclusions yet, but I think intermittent protocol might be well suited to replace continuous workouts when you can’t get your cardiovascular system ramped-up.

      What I mean, for instance: I went into a workout where my HR was depressed and I couldn’t even hit 90% VO2peak during a 3min high intensity interval, before my legs just ground to a halt. But I could sustain that effort for 30s microbursts which allowed my CV system to eventually ramp-up to that 90% target. So the 30/15 workout could be well suited as a ‘priming’ workout, or even a single set before continuous intervals. Just a hypothesis for now!


  2. Just started a polarized training base based on everything I’ve read here, just wondering – how are you defining the “20” in 80/20? Let’s say you did 10hrs weekly, does that mean 2h you’re in Vo2max intervals? That would be impossible! For me anyway. I’m doing the Lisboa protocol for my intervals and I’m only getting around 30-40 min per week, max. Or does the 80/20 mean “days”? Ie. 4 days long base rides and 2 days intervals?

    Thanks Jem!


    1. Hey Edmund. You got it at the end – the ’80/20′ refers broadly to ‘session intent’ and not to volume or duration. The ’80/20′ reference is just a frustrating holdover from when the most advanced training metrics were hand-written journals…

      If you’re training 5 sessions per week, 20% of that is only 1x high intensity workout. However if you’ve read some of my other posts, 2x high intensity per week seems to be ideal, then fill in Aerobic volume with whatever remaining time you have.

      Looking at minute-by-minute duration, I typically see <10% spent at high intensity. So if you’re getting say 2x workouts of ~30min duration at VO2max during a 10hr training week, that’s right on target!

      I think the Lisboa protocol is spot-on for VO2max. I’m seeing real VO2 data right now that seems to confirm that I’m up above >90%VO2max even as my power decreases from ~430 to ~380 through the interval.


  3. Awesome. Such good explanation & clarification! Really helps a newbie like me! Just started cycling this summer!

    Thanks as always!


  4. Great chart!! I’m really impressed how you develop this chart.
    I would like to test some workout and this chart could help me a lot, could you share the code?


    1. Thanks Alex,

      I won’t export the chart just because it’s a mess of old experimental expressions.. but it’s based on Donny Ki’s ‘Matches in each iLevel’ default chart. I’ve modified it a bit, but the main addition is the VO2max Power expression.

      This will give you the VO2max Power bars:

      if((@VO2/@VO2max)>=.9 AND ewma(bikepower,25)<levelfrom(“cogganoptimized”,8),ewma(bikepower,25))

      and workload in kJ:
      sum(if((@VO2/@VO2max)>=.9 AND ewma(bikepower,25)<levelfrom(“cogganoptimized”,8),ewma(bikepower,25)*deltatime))/1000

      You can probably figure out how to report time & %time from the default expressions.

      Hope that helps!


      1. Thanks Jem it worked, now I have to replace cogganoptimized with cogganclassic, but it is very useful.
        It could be also interesting to apply in running with power, do you know if is there a way to create personalized index?

        Anyway great blog


      2. Yeah I kind of use a mix of iLevels and my own tested physiological thresholds to create the ‘energy systems’. iLevels should get you pretty close across the board and will probably be better than Coggan Classic zones especially above FTP.

        I haven’t explored running power expressions at all. The VO2max formula in WKO4 is based on the ACSM estimate of VO2 from cycling power. You might be able to find the equivalent formula for running power. The experts on the WKO4 Facebook group might be able to help you out there


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