Cadence override for workouts

I was doing a workout on erg mode today, and there appears to be a weird feedback loop when you drop below the workout’s target cadence (or possibly it doesn’t actually have to do with the workout’s cadence but I’ll explain in more detail).

Basically, on the “recovery” or low output sections, the erg mode kept increasing the resistance, apparently believing that it needed to do so to increase my power. The problem is that the increased resistance forced my cadence down and made it harder to produce the requested power, which then caused the trainer to up the resistance more, until I’m in a situation where I’m grinding away at 30 rpm and 140 watts (not real numbers, but generally like that) even though I’m supposed to be holding 210 watts, which I can do easily. Once I turn off erg mode, I can sit at the requested power output (e.g., 210 watts) indefinitely, albeit at a lower cadence than the workout calls for (which is what makes me think this is cadence related).

Is there a way to simply tell the trainer to stop increasing the resistance based on cadence? It’s totally counterproductive: “Having trouble turning the cranks at 90 RPM at this resistance? How about I increase the resistance…will that help?”

Also, I’m 6’3" with long legs and spinning at 90rpm and above is just…hard for me. I don’t spin that high.

I see that a feature like this was discussed in the past, but that appeared to be more about ensuring that you earn your workout “star,” and not this weird erg mode feedback situation.

Hi @Peter_Nagle

Welcome to the forum.

What you describe sound like the Spiral of death. All About Erg Mode in Zwift | Zwift Insider

What trainer do you use?

Yes, that definitely sounds like what’s happening here. It’s a Saris trainer (unsure of model at this moment).

Wouldn’t it be helpful to be able to adjust the target cadence on workouts, like we can adjust the FTP bias? I’m just not a 90-120rpm rider - I’m more like 60-100. It totally borks my ability to use the workout if I must abide by the high cadences.

And I don’t think it’s a fitness thing. My zFTP at the moment is 250, yet I’m getting into the SOD at like 200 watts. ERG off and I’m riding at 65-70 RPM at 250 watts no problem.

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60 RPM should not be a problem for the Saris H2 or H3.

I use the SARIS H3 and have no problems doing workouts at 60 RPM.

Also Zwift does not do anything with cadence it is only there to make the avatar’s legs move and so that you have a onscreen display of RPM

Hmm. So maybe the “spiral of death” is a trainer-specific ERG thing? Because I know Zwift doesn’t really do anything with cadence, but the description of the SOD indicates that it IS a cadence-based thing.

Yes the SOD is the trainer trying to increase the resistance because your power is to low. If your cadence drop so does your power so it is sort of related to cadence.

What gear do you uses when using ERG.

With Zwift workouts, cadence is just a “suggestion”—the workout is focused on power. If your power is on target given your cadence, but then you reduce your cadence (because you’re tired or distracted), Zwift tells the trainer to increase the resistance (to “help” you maintain the target power). But if you respond to the increased resistance by further reducing your cadence, then Zwift again tells the trainer to increase resistance, which of course makes it more difficult to maintain cadence. And so on—the spiral of death.

I’m my experience, at some point, Zwift realizes what happened and turns off erg mode until you work yourself back to the target power.

Completely agree @Peter_Nagle , I’m about 6 foot and mid 80’s is quite fast enough for me, it’s like when they say stand up for a cadence of around 65 rpm, why, I can do that site happily sat down, it’s very rare I stand up when riding in real life, so why do it on zwift

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