Adding Z2 - do it before or after intervals?

It’s not uncommon for me to add time to workouts to get some Z2 time logged. I generally do this before the intervals because once you switch on the nervous system for intervals it alters the body’s state.

However, I was thinking this past week, might it be just as good to ride Z2 depleted and tired? Or perhaps alternate? One set of intervals you load the Z2 before, two days later you do the Z2 after?

Any thoughts or science on this that you folks can give me feedback on?

I think you over thinking this. Before or after is just not going to make a perceptible difference.

I just read a study about microdosing of resistance exercise and the conclusion was that 8x15minutes sprinkled throughout the week was same as 4x30min or 2x60min.

In the end, your performance is going to be dictated by the total volume and the training load you achieve. So just add the extra volume whenever you can.


This is a question I was going to pose to @Jonathan for the AACC. I believe that it’s “best” to do your Z2 first, but I’d love to know what the literature says it anything?

@The_Cog is there any direct comparison/science already out there?

The caveat being VO2, I think that there’s also the part of being able to generate a larger stimulus when fresh. Again, whether it’s more beneficial than a lower stimulus stacked on top of the endurance training stimulus I don’t know the definitive answer.

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Like many things the answer is really “it depends”.

If the object is to hit the intervals as hard as possible, then do them first when you are fresh. Then tack on the Z2 after. Do this consistently and you will add a lot of overall volume and the accompanying benefits.

However, if you are training for fatigue resistance, then there can be some value in doing Z2 first. For example, you could do a set amount of KJ first, say 2000, and then hit your intervals and see how you perform. A big difference between amateurs and elite athletes is fatigue resistance. The closer you can get your “fresh” numbers during the late ride intervals is a great way to assess your fatigue resistance.


^^^ this

I guess it depends on how much Z2 the OP is talking about. Tacking on 15 or 30 minutes to a session? or 2000kj which is several hours of Z2 depending on the FTP.

I’ve read about things like “tired 20” (20 minute power after say 2500kj. The question is, do you build this by doing intervals tired or by doing intervals fresh?

I’m typically adding a total of 45-75mins onto a TR ride. Not hours. I have a couple rides a week that are scheduled at 2+ hrs and one of them is usually 3+.

I think in that situation is probably makes the most sense to tack it on at the end and do as much Z2 as you have time to do and fits your schedule.

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In my 2021/22 season I (nearly) always tagged on some Z2 at the end of all workouts, ranging between 15-30mins, I averaged an extra 1.5 - 2hrs / wk Z2 work this way

My thinking was not to affect the quality of the workout itself by doing before but to do after when already fatigued / depleted.

I’m not saying it was directly responsible but that was my best season.

The science says before, apparently it can take 30 minutes after a high intensity exercise before you can start burning fats again but i never looked in how they determined this (in vitro or in vivo)


But if workout’s goal is to hit hard intervals, I would prioritise it over burning some additional fat :thinking:


Also, the goal of Z2 is, imho, not to burn fat. It’s to stress those slow twitch fibers. Still using the same, before or after.

I would say, it doesn’t really matter, but it depends on what you’re really training. So depending on your goal, before or after could both be “correct”.

Please post this study. Sounds like bro science. I’ve been tested in a lab 8x and have never come to any conclusion other than carbohydrate / fat utilization tracks very closely with power output. Doing a vo2 interval did not blunt fat usage for 30 minutes.


You will have the most muscle glycogen, PCr reserve, and least fatigue at the start of a ride, so you will have the most potential for making higher power numbers during your intervals at the beginning of a ride. The question is whether or not you believe being able to complete your intervals with higher numbers is more or less beneficial than completing them when you are already fatigued.

IMO, doing intervals at the beginning of the ride, or spread out evenly during the ride, is preferable over doing them all at the end.


Got it from a Stephen Seiler tweet, not a study but he’s not some bro scientist. (there are additional tweets from eg Alan Couzens and Inigo San Milan that >2 mmol/l blood lactate you cannot burn fat)

I heard the same from Inigo San Millan’s GCN interview. He talks about doing some hard intervals at the end of Z2 for endurance and VO2max training benefits and mentions that doing it the other way won’t give the same endurance stimulation.

That said, I’m totally with @Kuttermax and others above that it depends what you’re after. If you just want to increase the TSS I’d do it after hard intervals as it’s easier. If you want fatigue resistance then start doing intervals at the end. A lot of pros train that way e.g. a 6 hour ride might be 4 hours easy/z2 then 2 hours with intervals at the back end.

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If it’s part of a real long ride, Kolie Moore says you can do your (threshold / sweet spot) intervals spread throughout multiple hours of riding. The adaptations are still there. But you have to do it in one ride, not split it up across separate rides (two-a-days).

I don’t know if he’d say the same for VO2max intervals, though I suspect not. The first interval or two don’t really get you breathing as hard as the later ones, so I would keep the VO2max intervals as one block.

For shorter rides, where you’re just taking on an extra 15-45 minutes, I would do the Z2 first, for sure. As stated above, the body will be in a heightened state for some time after the intervals that will affect the Z2 time. Also, race winning moves more often than not occur late into the race. So it’s more race specific, which is a good thing.

For those worried about Z2 affecting your ability to hit your intervals correctly: if that actually happens to any significant degree for you, then you’ve got an inflated FTP/Z2 or a weakness that you need to address. And guess what’s a good way to address it? Training your weakness.


Z2 after 75% of the time (the non-science qouted is BS in this thread, doesnt exist unless someone whats to post a link, I’ve spent ages looking), depends on the goal of the session where you put it.

Do your heart rate always recovers perfectly after VO2max intervals? You never have trouble sleeping after a hard race or intervals close to bed time?

I think we can conclude something from experience

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Exactly, your comment proves my after 75% of the time comment. More bang after intervals without the muscular damage etc.