Originally Posted by
genejockey
Death spiral. In Erg mode, it tries to keep the power constant, so if you slow your cadence down, it increases the resistance, and if you're unable to put out that power at that cadence and slow down some more, it will keep increasing the resistance till you grind to a halt.
What the hell kind of workout are you doing, anyhow?
This. Keep cadence up in ERG mode as best you can or at least constant. ( remember power is essentially force * Cadence ) One thing to try to see how it works with your trainer is to keep a constant cadence and let the system adapt power for you. It take a second or two, but may help. For big power swings like Z1 or Z2 to Z4, it helps to change a gear or change cadence in the first few seconds of the interval on the way up and the way down.
But also Zwift will disengage ERG if you just stop pedaling. It will resume ERG mode shortly after you start pedaling again and should tell you so.