How to change intensity to match TSS between 2 rides

I’ve got a test in front of me next Saturday but, I’d like to swap out

  • Tapers (for me duration 00:46:50, TSS 57, and IF 0.85) with
  • a reduced Defender (for me duration 00:58:57, TSS 82 and IF of 0.92.)

I want to do this on Feb 28 (to ride as a Domestique for Sir @Emacdoug on the last day of his totally bonkers Daily Defender in Defence of Sir Dan).

To keep the training/rest equal is this as straightforward as reducing the intensity of Defender to 70%? So, Defender TSS 82 x 70% = 57.4?

I realize these are totally different rides with totally different aims. I just want to keep the load the same. TIA :pray:

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The best way to find out is to ride Defender today at 70% and see what the TSS comes down to.

We all know how much you love that workout :+1:


Yknow. Normally I’d agree with you and do exactly that. Riding it at 70% is not daunting in any way (as a single ride that is :stuck_out_tongue: ) However, I’m committed to something that requires me to keep my training load as close to the same this week and next as possible.


TSS scales with the square of the intensity factor (IF).
So for Defender (IF=0.92, duration 59 min) at 100%, that would give: 0.92^2 * 59/60 * 100= 83 TSS.
Defender at 70% would give: (0.92 * 0.7)^2 * 59/60 * 100 = 40 TSS
If you would like to end up with a TSS of 57 you should ride Defender at an IF^2 of: 57/(100 * 59/60) = 0.58 IF^2. So you would need an IF of sqrt(58) = 0.76.
This means you should ride Defender at 0.76/0.92 = 83%.
As a check: (0.92 * 83%)^2 * 59/60 * 100 = 57 TSS


Thanks @bartb and welcome to the forums!!

Daaaaaaamn, I like to do a little maths while I’m on the trainer (X minutes done, that’s Y% of the total ride, and you did Z yesterday, you can do this), but this is next level! What were you riding while you figured this out, Kitchen Sink?!? :wink:

Seriously though, very cool


I guess my bigger question is, given that IF and TSS are not something I can completely rely on since SYSTM workouts are based on my individual 4DP will the adjustment to 83% really result in the same load as Tapers at 100%?

I don’t know if system uses a ‘pre-computed’ value for TSS for each workout or that they compute it for each rider based on their 4dp. But whatever they do, this scaling would result in the same adjustment. Maybe you can find the TSS for a previous tapers session?
But in the end it doesn’t matter. You scale defender towards the TSS as intended by your plan. However, these 2 workouts are totally different regarding their intervals, so as stated in your link, TSS is not the only metric that matters.
But in my opinion, scaling down is OK in this case.


Oof, I don’t know about 83%. Are you trying to ride it in Zone 2 or Zone 3 or Zone 4?

I say this since I’ve been toying around with my own percentages from ride to ride and day to day to see how it feels.

But then again, when was your last FF/HM and how do you feel your current actual fitness compares to those numbers?

I did my last FF the beginning of Nov and then did HM middle of December and hit lifetime bests. However HM always tends to overestimate my numbers by 5-10w (it varies). Then I took 2 full weeks off. Then I did 3 weeks of spotty riding with mostly Zone 2 or recovery rides. Only really added any intensity and a full week of riding the last full week of January.

So, when I did Defender at 100% on February first I was NOT in the same shape as the numbers I was riding to and it was the hardest Defender effort I’ve ever done. Even 85% is still really difficult.

Hence why I ask how fresh and how relevant your FTP and MAP numbers are.

Defender at 85% for me is still low Zone 4 and 80% is the dreaded Zone 3. For me to do a Zone 2 effort in Defender I would need to drop it down to 75% (high Z2) or 70% (mid Z2).

Check out my Z1-2/Z3-4/Z5+ graph from for the end of Dec thru this today.

That’s more yellow than I’ve ridden in a long time. And a lot of those Defender sessions are at 80% or 85% which are still a lot of Z3-Z4. I usually try for 80/20. This is been closer to 60/40. And this week looks more like 40/60!

I don’t want to belabor the point any more. But definitely be sure the 4DP numbers you’re basing your percentages on is accurate. Mine sure aren’t. lol. Mine is definitely much higher than my current fitness. And doing Defender at 100% on the 28th is going to brutal.

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The other problem here is that these are such different rides. Tapers is a bunch of short intervals with lots of Z1 or bottom Z2 in between. Defender is mostly sub-threshold.

For me, Tapers is .77IF and Defender is .9IF. And I couldn’t tell you how to make them even out based on the wide differences in ride profiles.

But based on 24 days of experience… I would consider recommending that you do something like this:

Do the warm up at 100%.
Set MAP 100/95%
Set FTP 75/70%

Then you’ll get some good warm-up. But the intense parts only lasts 90 seconds, and only 30 of that is above threshold - not too long. You’ll get some good intensity but not too much with the 2 minute MAP sections. Then plenty of Z2 during the rest of the intervals, and Z1 during the recoveries.

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Thinking about something just like that. Thanks for the suggestions Sir!

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I guess you are trialing Defenders at 70% to see what it gives you, then riding it again at the presumed % again and then subbing it in again to keep the weekly load the same :fist_right:t2::+1:t2:

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Yes Sir!