Why is it so very difficult to keep power between 100-105 when tired in ERG?

Why is it so very difficult to keep power between 100-105% in ERG when tired? When I want to give it a bit more my trainers starts spinning out and I can’t keep up spinning unlike when I tire but the power requirements are even higher and the amplitude of power just gets bigger around the required target

  • Can you explain this more?

  • If you are aiming to deliver more power than the target, while using ERG, you should use thw Workout Intensity setting. “Spinning up” is only goind to end up qith a faster cadence once thw trainer and ERG adjust together.

It sounds like you may be trying to apply Resiatance mode adjustments while using ERG mode, and that won’t work.

Maybe you chan share a workout or screenshots of a workout showing the issues?

What trainer are you using and what gearing while in ERG?

kickr v5, 36T front, somewhere in the middle of the cassette that came with the kickr

So when I tire close to threshold and feel ERG mode ramping up the resistance I try to give it my best but it always results in my just bobbing all over, the resistance and power going down, but when the reqirements are even higher I can increase the spin and resistance matches up so the power requirements are met

at that stage I’m already really tired…

Very interesting. The zoomed in section of the first segment is seeming decent until the last quarter. Notable to me the relatively high cadence show (115avg, 134 max). Is that normal for you in an over-threshold effort like that?

Could be a sign of fatigue more than anything, coupled with a power level that is a particularly challenging for you? The highlighted segment is mid workout, and the subsequent ones are also troubled from the higher level picture. Would you say you were cooked and struggled in the rest of this workout? How did you rate it?

Looking at the second workout picture, there is a pretty consistent decay in your cadence from start to end of the many of the main segments. These seem to have a more typical cadence around 101/110 avg and max. How did your feeling in legs, lungs and heart compare here vs the first pic?

Is the delta between both pics the effect you are talking about with that Threshold plus level (pic 1) and above that (pic2)?

I am not sure without a deeper dig into the actual workout data if this is more ERG related vs fatigue. The Kickr seems to respond pretty well based on my K17 vs H2 and Neo2 relatively speaking. I can’t say I notice a difference in response at Threshold vs any other level either.

This is interesting because ERG mode doesn’t really ramp up resistance.

What it looks like to me is your cadence is causing these issues. You start high, fatigue and slowly go down. This might feel as ramping up the resistance because a lower cadence will require more torque to keep the same level of power.

When working in ERG mode you should really focus on keeping your cadence as smooth as possible for the best feeling workout. Big differences in cadence make the workout harder and you’ll see these spikes in power you’re experiencing.


Try the big ring if you have a 2x crank. Without looking closely, it seems you have a bit of Kickr spiral of death from reducing cadence. You could also try turning off Erg.

Erg doesn’t work the same as outside - I mostly train outside and actively use cadence variations and force modulation to keep power smooth.

I’m stuk in ERG mode for the moment as my right shifter is still broken. I could try the big ring but wouldn’t that make things worse?

When I start feeling tired I try picking up cadence/power but when the target is around FTP this results in my overshooting, the resistance falling and spinning out with a cadence of 130+ whereas when the target is higher I feel the trainer quickly adding resistance again

  • Using a faster gear in ERG can give more functional flywheel speed and related inertia.

    • This can smooth out the power delivery for one thing and make it more likely that you keep your stroke more consistent around the full path.

    • Additionally, faster flywheel speeds make it harder for the trainer to apply fast changes to the resistance. It partially handicaps the system and effectively can smooth out the power from this aspect because it slows the functional response time of the trainer.

Those are two key benefits of faster flywheel speed with getting less change for a death spiral started. The other benefit that many like is that the “feel” is often more like riding outside from that faster flywheel. It is still “ERG feel” and different than using Resistance / Level / Standard modes, but it is a way to get ERG more useful for many riders.

When you do this, are you watching power and trying to “match the target”?

  • If so, you should stop that. Watching power and trying to “fix” is while in ERG is a recipe for problems.

  • I like to say, “Cadence is King” when using ERG. Meaning, you focus on your cadence and IGNORE power. Don’t even look at power. Just watch your cadence and try to hold it as steady and smooth as possible. This will allow the trainer and controlling app the best ability to keep everything rolling as intended.

  • It’s fine to alter cadence for things like standing efforts or just to mix it up, but make those changes deliberate and relatively short in step duration. Once you get where you want to be, hold that RPM steady again for whatever duration you want. SMOOTH cadence can solve many problems with ERG use.

  • Fatigue is real thing, and if you start slipping cadence, you need to get on top of it if that is your goal. But try to do it via more gradual effort change on your part, rather than “spikes” to kick over. ERG doesn’t handle those spikes well to begin with, and they take a real toll on your body which is a double whammy.

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Good question and some great answers.

I am having the similar experience that VO2Max intervals are much more difficult in ERG mode when I am tired compared to SIM riding

I find it hard to “get on top of cadence” when I am tired, and I end up in a downward spiral with ever slower cadence instead

I am not using TR currently, though. But it seems there is a general issue with hitting the right cadence for HIT when fatigued in ERG mode.

Echoing prior answers, but for sure use the big ring, the changes in resistance are much more dramatic when the wheel speed is lower.

Also, I know it seems easier to go with a super high cadence, but I would definitely try to find one you can hold steady the whole time, or at least steadier. I get caught in this trap sometimes around threshold. I wonder why I’m so tired and realize I’ve been spinning at 100+ needlessly.