How to estimate contributions to high and peak stress during a ride?

I have an old Garmin that doesn’t support the new XSS buckets data field, but want to be able to get close to the targets as forecast. Is targeting focus time + total XSS accomplishing the same thing? E.g. if the forecast is for a “Polar GC Specialist (8 minute power)” ride of 122 XSS, will aiming for those parameters get me generally to the forecast low, high, and peak stress? Seems like it should.


Also experiement with the workout editor to get a feeling for which intervals contribute how.

1 Like

Yes, you can ride to a target Focus Duration and strain goal for the day by monitoring Xert Connect IQ data fields on your Garmin. Namely, Focus/Difficulty. TTR/TTE, MPA/Power, and XSS/XEP.

In your example, you would ride irregularly spaced intervals (terrain and traffic permitting) at your 8-minute power or a bit above. Then rest and repeat for however long it takes to accumulate 122 XSS.

This thread dives into the concept and includes a link to a YT video demonstrating the process –

As you practice riding to Focus, I think you’ll find you can closely match the target strain ratio and Focus for the day.
The advantage to XSS Buckets is that is combines the components into one data field/app and provides a visual XSS ratio bucket to fill.

Another option is to run Autogen to generate a simple workout that matches today’s goals.
View the workout details and note number of intervals, watt target, duration, and rest-in-between time then ride intervals similar to that during the ride. No need to push the workout to the Garmin but you could if you want to. Otherwise, the intervals don’t have to be exact to reach the Focus Duration and strain goal for the day. For example, Autogen might show 3 sets of 3 intervals at X watts for X seconds separated by X minutes rest-in-between. At some point during my ride, I’'ll insert 9 intervals at approximately the target watts with suggested rest-in-between.

1 Like

Thanks, @ridgerider2. Helpful suggestions!

After a bit of thought, I can see how playing with the workout editor could give me a good idea of power targets, thanks @Beutelfuchs.

Good thread … so Wahoo users … none of this applies - is that right?

One extra thing - if one was to buy a Garmin in a few years, do the Xert calcs work on the assumption that strain is second by second based on power? The reason I ask is, energy systems don’t quite work that way … once the body kicks in to sugar mode (eg threshold efforts or heed ever the cut off point is for each individual), it doesn’t come down from that very quickly. So in many people’s cases, once the body is in high energy mode it can take quite some time to return to burning any fat.
I wondered if there was a similar consideration for when working at high effort levels, at what point does the effect in the body start to reduce, or is it instant. I don’t k is the answer to that question - so the sports scientists here might have some testing/papers on this maybe?

I was pondering this very thing yesterday as I was doing my intervals on a long-ish ride. Do only one kind of ride or the other, or try to mix intervals and low intensity? According to Inigo San Milan (and like you say), once you’ve gone from fat burning to glycogen burning in a significant way then getting back to fat burning will take quite a bit of time. How much time? I’ve never heard that addressed in a meaningful way - it’s very hand-wavy. I recall the Fast Talk podcast discussed this topic sometime within the last few months, and I believe I remember they played a clip from Armando. I’ll have to see if I can dig it up.

1 Like

@jw66 yup. and the relationship between ‘strain’ and those energy systems becomes a thing.

And of course then there’s knowing what your own personal fat vs sugar crossover point is without having lab testing available.

At which point do we just stop faffing with this stuff and ride our bikes :rofl:
I reckon I need food … eat, I need to drink regularly, so do that too. Stop for ice cream when it’s hot, don’t go nuts when you’re in a long ride if you wanna last longer.

On the ‘do one type of ride vs another thing’. I tend to do that if I’m indoor training. One VO2 (we used to call those intervals before we had labels), one ‘syrangth’ (aka low cadence work), one at a pace I could ride two hours for …. job done
Outside … different story as I don’t have a bike with enough gears to allow me to get up hill without going above threshold unless I ride in walking shoes and walk a lot. So every ride I do will have threshold work. But I do try and limit ‘unnecessary’ hard work on ‘generic/endurance’ rides to make them ‘one tbing’ sometimes.

That was debunked.

Not according to Andy Coggan. Check his interview at Inside Exercise podcast:

Thank you both. I’m very glad to have that input, because I couldn’t reconcile San Milan’s assertion (once you’ve done work at higher power endurance adaptations go out the window for some unspecified duration) with all the work I was doing at lower intensity on that ride. It did not make sense to me that the much greater amount of low intensity work would not contribute to a training effect just because I did some 30s intervals at 2x TP power.

@Jomavami I’m listening to that episode now, thanks for the link!

1 Like

I think there is something more that we can understand when you look to quantify lactate production and then how it’s used. Remember that lactate is burned aerobically, just like fat, in the mitochondria. So if your blood is flooded with lactate from a major effort, it will be used as fuel for subsequent exercise by the mitochondria. But it doesn’t take long for it to drop to lower levels (the return of MPA from fatigued to fresh does not follow some sort of decline in blood lactate. These are separate.)

Lactate has one of 3 fates:

  1. It is taken up during exercise by the working muscles
  2. It is taken up by other organs and basal metabolic functions
  3. It is taken up by the liver to put glucose back into the blood to maintain blood glucose levels (something I refer to as just GNG for gluconeogenesis).

(1) uses the most lactate. (2) uses very little and (3) uses up to a ~1/3 of (1) but depends on training status, liver glycogen levels and blood glucose levels from carb ingestion.

Generally, lactate doesn’t last long if you’re recovering at a high intensity close to LTP (1). If you do nothing and stop, it will take a lot longer (2 and 3). You can get back to burning fat pretty quickly if you do (1) and you’re still keeping your mitochondria active and under strain when you do this. If you stop, then yeah, it will take a bit of time.

A lot also depends on the type of athlete you are. If your HIE and PP are larger than other athletes, you can generate more lactate and therefore (1) will take longer. If your HIE and PP are smaller, it’ll clear far sooner. This is the VLAmax training and concept you may see used elsewhere.

I’ve seen a lot of athletes get super strong with workouts that have sweetspot under fatigue. We have quite of few of these in the library. These intentionally build up lactate and force it to be used aerobically with higher recovery “sweetspot” intervals. The puts additional strain on the mitochondria to use the lactate to produce more power. If these are done in a fasted state, you could in theory see (3) increase since blood glucose drops and the liver, if empty of its own glycogen, would resort to GNG to maintain blood glucose. The benefit of (3) is that you’re in effect eating back your own glucose from muscle glycogen that you burned. The process can produce a significant amount of glucose into the blood in well-trained athletes allowing athletes to perform better deep into rides.

So although “burning more fat” is a good thing in general, there are a few more aspects to consider wrt exercise metabolism.


To answer the OP question, this is something I think many Xert users will learn to do over time. The entire concept of low, high and peak XSS is totally new and training them in this way has never been done before. So we’re learning about this in the same way you are!

One thing that I’ve done, when I’m not using Buckets, is the put a similar outdoor ride into my plan that I’ll be doing. I’ll then view the low, high and peak XSS and mentally assess how this might play out. I can interrogate the previous ride to see how these were achieved. For example, anything with a lot of peak XSS had a lot of sprinting in it. That’s pretty obvious. If there’s a lot of high XSS, then I can look at where they came from and then map out where in my ride I’d do the same or similar. Sometimes it from a long climb or rollers or a section where we chased that I see the yellow and orange on the chart. I can start to develop a feel for what 10 high XSS is like on a 1 hour ride or on a 3 hour ride, for example. There’s no simple way because you’ve got 3 levers all working to move your pedals. We could conceivably give you power targets but so much will depend on how much longer will you be riding and how many opportunities will you have to do intensity or go easy. Other than give you a workout, it’s pretty challenging to give precise instructions, at least we haven’t yet cracked that nut.

So use previous ride low/high/peak XSS as your mental guide as you ride and compare these with the actual low/high/peak XSS from your completed ride to gain an intuition on what you’ll need to do. You’ll then develop a feel for what’s needed and also understand how you’ll need to train to increase your power.

1 Like

Thanks, @xertedbrain. I understood and really appreciate both posts – well explained! I’ll have to come back and read them again in a week so that they really sink in.