ERG Mode for Indoor Cycling: When to use it and when to turn it off

By Jim Rutberg,
CTS Pro Coach, co-author of “Ride Inside”
and “The Time-Crunched Cyclist”

For cyclists using smart trainers and internet-enabled cycling apps, one of a smart trainer’s core capabilities is to externally control and adjust the resistance a cyclist experiences. Of the multiple ways this can be applied, ERG Mode is one of the most important. Here’s how it works, when you should use it, and when you should turn it off.

What is ERG Mode?

Erg mode is short for “ergometer mode”, a setting used by smart trainers and apps like Zwift, Wahoo X, Trainerroad, Rouvy, Fulgaz, etc. to achieve a prescribed power output by adjusting the resistance you experience at your chosen cadence.

Power output is the product of torque (force applied to cause rotation) and cadence. If the smart trainer is set to maintain a power output of 250 watts and you decrease your cadence, the trainer must increase the resistance. If you increase your cadence, the trainer must adjust to decrease the resistance you experience.

ERG Mode vs. Level Mode vs. Sim Mode vs. Resistance Mode

Smart trainers sometimes use different brand terminology for these settings, but essentially, the differences are:

• ERG Mode: Prescribed power output that adjusts resistance based on changes in cadence, and follows time-based structure.
• Level Mode: Attempts to match “road feel” or the resistance curves from traditional wind or fluid trainers. The resistance increases exponentially with increased speed.
• Resistance Mode: Similar to gym-based spin bikes that clamp down on a spinning flywheel, this mode holds resistance constant even as cadence changes.
• Sim Mode: Resistance adjusts based on terrain as you follow a route/course. Initial ride characteristics set by rider weight and bike/environmental parameters. Used for ‘free riding’ and e-racing in apps like Zwift, etc.

When to use ERG Mode

ERG mode is very useful for structured workouts. When you select a structured interval workout from a library in your favorite training app, erg mode will automatically change the resistance when intervals start and stop. Your resulting power file will look technically perfect. A 10-minute interval at 250 watts will be exactly 10 minutes long and your power output will stay consistent at 250 watts. Your recovery periods will be similarly enforced at low power outputs.

If you are working with a CTS Coach or any coach prescribing structured workouts through TrainingPeaks, you can export the structured workout to be used in erg mode on a smart trainer. You can export directly to an indoor cycling app (Zwift, etc.) or download to most bike computers (Hammerhead, Garmin, Lezyne, Stages, etc.).

You can also use erg mode to manually set target power outputs while you ride the trainer. This is not as common as using a structured workout or the Sim or Level modes. However, it can be useful for someone who struggles to stay at a Zone 2 or recovery pace in ‘free ride’ environments.

Gear Selection for ERG Mode

If erg mode adjusts the resistance you experience based on your cadence, does it matter what gear you’re in? Kind of. If you are training for flat, high-speed events like time trials, triathlons, even road races and criteriums, you’ll want to use a big gear in erg mode. This mimics the inertia you’ll feel in the pedal stroke in the real world.

Similarly, if you are training for steep climbs, use a smaller gear, like you would on the road or trail. There will be less inertia to keep the trainer’s flywheel going when your pedals are at the top and bottom of the pedal stroke. This is similar to the real world, where you decelerate slightly between downstrokes on steep climbs.

If you are doing interval workouts with very short intervals and short recovery periods, consider using a small gear (like the climbing gears) for intervals. This will help the trainer adjust the resistance faster to keep up with the structure of the workout.

Shifting while using ERG Mode

Although you don’t need to shift gears while using erg mode, there may be times when you want to. Remember that erg mode will increase resistance if your cadence drops. Sometimes cadence drops due to a moment of inattention. Now the resistance is higher and you’re grinding along at a cadence lower than you want. If you shift into an easier gear and increase your cadence at the same time, you may get a few seconds to reset your cadence before the trainer readjusts the resistance. Just keep an eye on your gears, because you can end up cross-chained if you keep downshifting.

Some riders will also shift into a bigger gear to stand up on the indoor trainer, just like you would outside. This is because your cadence is likely to drop when you pedal standing up, and you have your bodyweight to create greater torque. Just remember to shift back to an easier gear as you sit down, otherwise it can be difficult to overcome the resistance to increase your cadence.

When to Turn ERG Mode Off

As a coach I love the precision erg mode provides but I know there are serious downsides to overusing it. I’d even argue that ergometer mode can do cyclists and triathletes more harm than good. Here’s when and why you should turn erg mode off:

Turn off Erg Mode for maximum effort intervals:

Erg mode works great when you want to target a specific power output, like during Tempo, Sweetspot, and Functional Threshold Power intervals. For maximum effort intervals like sprints, anaerobic capacity intervals, and some types of VO2 max intervals, the goal is to reach as high a peak power as you can. For these efforts, use Level mode so the resistance increases exponentially as speed increases (as it does outdoors). Depending on the trainer, you may need to adjust the resistance curve setting in Level mode so it matches the gearing and cadences you would typically experience outdoors.

Turn off ERG Mode to learn to pace race efforts

As I wrote in Ride Inside, “There is a difference between being able to withstand the effort required to ride at 400 watts for five minutes and having the grit and internal motivation to reach and sustain 400 watts for five minutes on your own.” Having the physiology to produce power doesn’t mean you have what it takes to conjure that performance when it counts.

From a coaching perspective, I have athletes perform intervals in both ERG and Level modes, even when the interval structures are identical. In other words, I might have an athlete doing 3 x 10-minute FTP intervals twice in a week do the workout in ERG Mode on Tuesday and Level Mode on Thursday.

More specifically, it’s important to consider the objective of an interval workout. During ‘extensive intervals’ the goal is to extend the time an athlete can sustain a target power. However, the goal of an ‘intensive interval’ is to increase the target power output. For both types ERG Mode can show an athlete they have the capacity to go longer or hit higher power targets. But then, it’s important for them to achieve those performances without the ergometer’s assistance.