You're riding in ERG mode. Maybe you pause for a moment, maybe you just slow down. Suddenly the interval is getting harder and harder. You look at your screen and think, "I know I can hold that many watts, but I can barely pedal." What's going on?
You've run into something we call the "ERG mode death spiral".
ERG mode makes sure you hit your target power for the current interval by decreasing resistance if you speed up and increasing it if you slow down. But achieving your target with higher cadence and less resistance is easier than achieving it with very low cadence, and very high resistance.
The "death spiral" starts when your speed drops, and the trainer cranks up the resistance in response. That big jump in resistance catches you off guard so you slow down, so it increases resistance, so you slow down etc. until you speed back up with one massive burst of effort, or else slowly grind to a stop. This can happen on any trainer capable of ERG mode.
- Avoid stopping and starting mid-ride, especially during tough intervals.
- If your workout includes a large or sudden increase in power, start speeding up a few seconds ahead of the interval change.
- If you're having an "off" day, try an interval workout in resistance mode.
- If it happens repeatedly, adjust the workout strength down slightly.
- Follow a training plan, including rest and recovery.