Standard deviation of power

I am using a Tacx Flux 2 trainer while in erg mode and running workouts from my phone.

It’s all but impossible for me to hold steady power across my intervals, yet other folks I see on Strava have their power matched exactly to what the session calls for without so much as the slightest deviation.

New to a trainer and interval training I’m willing to accept some blame, but something else has to be at play… Thoughts? Thank you.

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First off, welcome to the forum.

No need to beat yourself up dude. It’s likely that the folks you see that have super steady power could be utilizing a trainer that has some degree of “power smoothing”. Wahoo smart trainers for one have this and when enabled will make super smooth graphs even in instances where a rider might have a super uneven power profile. I’m not that familiar with the flux 2, so I’m not certain if it has a smoothing option.

When running in ERG mode, what you need to focus on is your CADENCE… Looking at your above graph, it looks like your cadence was a bit all over the place. If you focus on keeping it more consistent, your power should smooth out substantially. With a choppy and inconsistent cadence, the trainer is constantly adjusting to try to hold the power target.

Give that a try next workout and let us know out you make out!


What Will said. Ignore power numbers (trust TR to do the right thing) and just focus on cadence. At least for now with longer intervals as you get used to it.

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@jakeramirez your power looks great, exactly what to expect. Anyone with ‘perfect’ power is having their Kickr lie to them. Fake. Ignore the picture perfect fake power.


It’s normal for power to fluctuate.

Your cadence looks odd tho. Are you trying to vary your cadence to get power on target? No need to do that with a smart trainer in erg mode. Just pedal at your preferred cadence, and the trainer will adjust.

One other thing: best to ride in the small ring, middle of the cassette to allow the trainer to better track power. If you ride in big ring, small cassette cog, the power can fluctuate more.

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I think something might not be quite right as cadence looks a bit sporadic also.

It doesn’t have to be perfectly smooth to be effective. In fact if you ever ride with power outdoors you’ll realise the power varies quite a bit. It varies within a pedal stroke let alone between pedal strokes. Your output looks good.

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I used to have a Flux 2 and the power line tracked perfectly in ERG and almost perfectly in resistance if I pedal smoothly (I’m not saying this is realistic).

The above happened to me and it was drop outs between the trainer and TR/device IIRC. Maybe reach out to TR support, who will be able to diagnose and see a log of the interplay of signals/commands between your trainer and the app.

IMO it’s sub optimal to keep having drop outs on steady intervals. It’s like coasting for a few seconds, which I wouldn’t keep doing on the road mid interval. However I do agree with the others not to worry too much, as power was definitely within range and actually over target a fair bit.