ERG mode is something that confuses a lot of new Zwifters. When should you use it, and what exactly is it anyway? Here’s a quick explanation…

What Is ERG Mode?

Smart trainers have different “modes” which define how much resistance they apply while you ride. The two most common modes are ERG and Sim.

In ERG mode your trainer’s only job is to make you hold a particular wattage. “ERG” comes from Latin for “Ergo” which means “work”. ERG mode is literally forcing you to work at a particular level.

Example:

  • Your Zwift workout interval wants you to hold 200 watts for 10 minutes
  • If you are spinning at a cadence of 90 and putting out 200 watts, then slow your cadence to 60, your trainer will increase resistance so you are still doing 200 watts even though you are pedaling slower.
  • If you are spinning at a cadence of 90 and putting out 200 watts, then increase your cadence to 110, your trainer will decrease resistance so you are still doing 200 watts even though you are pedaling faster.

So your only job in ERG mode is to manage your cadence. You don’t need to worry about shifting (although it is allowed), or whether you are hitting your wattage target. You just need to keep your cadence where you want it, and the trainer will make sure you’re hitting the target power.

When Should I Use ERG Mode?

Use it for workouts where you want to hold particular power levels for particular intervals (which is most workouts). ERG mode is enabled by default if you begin a workout while using a smart trainer in Zwift. (Non-workout rides in Zwift are done in Sim mode, which applies resistance base on rider weight, road grade, and other variables to “simulate” riding in a virtual world.)

I’ve been asked if ERG mode should be used in races. First of all: this would be a little challenging to implement given Zwift’s event functionality. But even if you could do it, why would you? Racing requires constantly adjusting your effort to stay with the pack, attack on punchy climbs, ease off on descents, etc. ERG mode was not made for on-the-fly adjustments.

How to Disable and Enable ERG Mode in Zwift

You can disable and enable ERG mode from the workout browser screen by toggling the “Use ERG Mode” button.

You can also turn it on or off during your workout by clicking the up arrow, or clicking your mouse near the bottom-middle of your screen. This will bring up a menu which includes a button for turning ERG on and off (see below). (On iOS or AppleTV swiping up will let you access this menu.)

The Spiral of Death

If you understand how ERG mode works, you’ll understand what we like to call the “Spiral of Death”. This torturous event happens when you are in ERG mode attempting to hold a particular wattage, then your legs get tired and your cadence slows. In order to keep hitting the wattage target, your trainer will then increase the resistance (see examples above). This increases resistance means your cadence will slow even more, which means the trainer will pile on more resistance… until you feel like you’re pedaling through wet cement.

For a further explanation of all things ERG watch Shane Miller’s video below: