How tight should I be able to hold a power target?

Still somewhat new to TR and structured training and I’m looking at one of my upcoming workouts and wondered: how well should I be able to hold a power target to the number?

I know that fluctuation is expected and it’s not realistic to be able to hit a specific number for a duration without going over or under, but I look at the endurance sections of something like Kennedy

The watt fluctuation is only 3 watts, and while I do my best to hold a number, I definitely fluctuate more than that when trying to hold a single number :grimacing:

I do my training on rollers so I don’t know if that makes a difference vs a trainer where I’m bolted in place maybe??

How should I approach that kind of fluctuating power target?

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The watt fluctuation you are seeing in those endurance sections are, IMO, more about engagement than performance. If you did those stretches with only a consistent wattage, it would be pretty dull. Breaking them up makes the intervals “shorter”.

Fluctuation matters much less in endurance since it is a bigger target zone. Don’t sweat some minor variation. Our bodies aren’t that precise, as Amber used to say.


Don’t try to hold a single number.

That workout was probably programmed years ago (who knows), but the fluctuations in those endurance are actually designed to give you that message, not to be taken literally. Just meander around that value, maybe +/- 10 watts. You will not be able to hold +/- 3 watts, especially on rollers. And since you are on rollers (awesome), it is likely you won’t feel overly compelled to hold that number so much that you switch to ERG mode (mistake). ERG mode has its place, but you do not need ERG mode for an endurance section of a workout that fluctuates 3 watts because you have to hold those 3 watts.

Hopefully this won’t start a distracting debate, but I would argue you don’t need to hold a number that precisely ever, even when it’s not endurance. So then why is it programmed that way? Because it is software, you have to give some discrete value.


Yeah, I would just look at the high and low numbers of that entire block and try to stay somewhere within that, plus or minus 5 or so watts. Also, I’d set my smoothing to 10 seconds so that I’m not distracted by the constant up and down of the watts I see on screen.

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ERG is a little bit of a pain on some trainers not letting you fluctuate enough but if you’re using rollers you’ve no problem there @cschmitz . I do my work outs on resistance mode which allows substantial fluctuations but touchwood it hasn’t triggered a fail survey lately. There was certainly more than +/- 3w at time on my last workout.


Hey @cschmitz!

Looking at your setup (rollers, Rally power meter), you’re actually doing a great job at staying within the power targets!

Unlike most smart trainers, you don’t have ERG Mode and are relying on resistance; needing to change gears as you typically would while riding outdoors. Soooo, if your power is fluctuating on any workout, then that’s totally normal :slight_smile:

Dittoing @Power13, Our bodies aren’t that precise, as Amber used to say.

By the way, what rollers are you using?


Nice, thanks for all of the replies everyone :smiley: I figured the fluctuation range was ok, but it’s great to hear it for sure.

@Caro.Gomez-Villafane I’m using Action Mag Rollers from Minouta (link is to the resistance unit, I actually can’t find the link for the specific model I have on their site, but the image on the resistance unit is the one I have). They’re “dumb” rollers in the sense that there’s no resistance feedback and they don’t rock or anything, but they get the job done :). I have the resistance unit installed, but I don’t use it at the moment b/c I’m not topping out on my gears on my road bike.

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That’s not really true. Even if a trainer applies massive smoothing to show perfect power lines, the reality is that there is notable fluctuation in the actual power from the rider.

I’ve yet to ride or see a trainer that reacts fast enough in ERG to show “perfect power” as measured by a real power meter.

Point being that even with the best trainers in ERG, there will be constant power variations at some level and we’re talking more than a few watt swings.

Just as confirmation of what Chat said, here’s what it looks like when using a Kickr in erg mode (power measured with Quarq powermeter at the crank) at a steady 222 watts, without smoothing on:

Looks pretty smooth but when you zoom in power is actually fluctuating from 206 to 236! Even with erg mode there are continuous adjustments. I could probably see less movement if I used the Kickr’s powermeter but I prefer to keep my power consistent with what I see on the road. There may be more variation when riding at a lower cadence as well. I personally didn’t feel the variation in power, it basically all felt the same.

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It is with the Suito. I’ve not come across anyone yet that says that ERG runs smoothly on a Suito. I believe ERG does run smoother on other trainers and your statement is true there I think, so I delimited it to, a little bit a little bit of a pain on some trainers, rather than a broad statement about ERG on all trainers. But your right even the best trainers will have some fluctuation :smiley:


(There’s a reason why NP is based on a 30 s rolling average.)

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I train without ERG so I will take a look at the Outdoor version of the workout. The outdoor description will give you ranges. (I also do most workouts outside anyway)

Outdoor description for main set from Kennedy:

  • 20 minutes ranging from 157to 166.
    Actual range based on your current ftp.

I always do outdoor workouts within a power range. Choose a road / terrain that best suits the workout demands and do your best. Exact power values is just a feature of trainers needing a value for ERG. It’s not critical, and as others say, your body won’t care.

Exactly. Some people (I’m looking at you, Zwift forum) don’t seem able or willing to grasp that it’s physically (and logically) not possible for you to ride, say, a 10 minute threshold interval in Erg mode more smoothly than riding it in resistance mode if you focus on riding as smoothly as you are able.

Think about it. It’s literally impossible unless the trainer is controlling YOU!

Which it isn’t.

I guess some people just like being lied to.



If you work on grip strength, I’m sure you can hold that target power even tighter! :rofl: