ERG mode explained: what is it, how to use it and when you should turn it off

ERG mode is one of the key features of a smart trainer, but how can you get the most out of it?

Pro cyclist on a smart trainer using Zwift

Sales of indoor trainers have exploded, with major bike retailers reporting sales increases of between 500 and 1,000 per cent in the UK in 2020.

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Smart trainers account for a large proportion of these sales, where “smart” refers to the ability of a computer program or app to talk to the trainer and control the bike’s resistance without the need for a rider to shift gears.

One notable feature of smart trainers is the ability to ride a workout in ‘ERG mode’, so let’s take a look at exactly what ERG mode is, why and when you might want to use it, as well as the key advantages and disadvantages it can offer.

What is ERG mode?

ERG mode explained: what is it, how to use it and when you should turn it off
ERG mode is one of the key features of smart trainers, which can communicate wirelessly to computer programs and apps.
Simon Bromley / Immediate Media

ERG mode is a setting in training platforms such as Zwift, TrainerRoad and Sufferfest that fixes your power output by automatically adjusting your resistance to match your cadence.

Power is a calculation of torque (how hard you’re pressing on the pedals) multiplied by cadence (how fast they are turning). ERG mode uses the two in tandem to ensure you hit the prescribed power output.

As an example, if a workout requires you to hold 200 watts, the resistance will automatically increase if your cadence drops, or decrease if your cadence increases, in order to keep you at 200 watts.

This is in contrast with other trainer modes, where the onus is on you to adjust your resistance and cadence in order to hit your target power.

Perhaps not surprisingly, ERG mode only works with pre-built workouts because it requires a target power to be defined, otherwise the trainer wouldn’t know how much resistance to apply.

However, the latest indoor cycling apps offer a wide range of workouts and training plans, and also allow you to build your own.

Benefits of ERG mode

ERG mode explained: what is it, how to use it and when you should turn it off
ERG mode automatically controls the resistance of your smart trainer to match your cadence, in order to achieve a specific power output.
Tim de Waele / Getty Images

One of the big advantages of ERG mode is that you don’t need to think (much) about your workout, which can be helpful if you’re riding at the end of a tiring day. Just start the workout and pedal.

The only thing you really need to focus on is keeping your cadence in a comfortable range, and not varying this too much.

ERG mode is particularly appealing for interval workouts, and for good reason.

First, using ERG mode is helpful for people who struggle to pace their efforts and regulate their power. There’s often a temptation to go harder than planned over the first few intervals, which might mean you can’t complete the last few. ERG mode prevents this by fixing the power in the correct range.

Second, ERG mode can help you hang on over the last few seconds of an interval, where you may have ordinarily have given up. Think of it like an automated training companion, keeping you pushing right up to the last second.

By fixing your power to hit a pre-determined output, both during an interval and recovery, ERG mode also allows you to target specific training adaptations, whether you’re working on your VO2 max or improving your sprinting.

You can use ERG mode in conjunction with your training zones to set the precise output for a particular workout (training apps will do this for you), helping you get the most out of a short training session – one of the key benefits of indoor cycling.

While people tend to mostly use ERG mode for interval training, another important benefit it offers is keeping riders ‘reigned in’ during lower-intensity rides, including base training, where there can be a tendency to go harder than is necessary to stimulate the desired adaptations.

Drawbacks of ERG mode

ERG mode explained: what is it, how to use it and when you should turn it off
ERG mode is great for targeting specific training zones, but isn’t necessarily reflective of real-world riding.
David Caudery / Immediate Media

One major drawback of ERG mode is that it’s based on a fixed percentage of FTP.

However, FTP changes from day-to-day depending on factors such as fatigue, sleep, nutrition, hydration and so on. This means on some days your power targets in your workout might be a little too high, and on others they might be a little too low. Some apps, including Zwift, allow you to adjust the difficulty of an interval session during the workout.

Riding too often in ERG mode can also limit development of skills that are important in the real world. These include the ability to gauge your effort level and determine appropriate pacing, controlling your power output through appropriate gear selection and cadence, and have the mental fortitude to push hard entirely of your own volition.

While it’s great to be able to ride a workout without too much thinking involved, sometimes the focus needed in continually adjusting your own resistance and cadence to meet your power targets can add interest to a session.

So, switching off ERG mode every now and again if you use it often might be a good call if you’ve got a long indoor session to get through.

Spiral of death

Another downside of ERG mode is that intervals can sometimes feel harder, particularly if you start to fatigue and cadence drops outside a comfortable range.

At the extreme of this, you can get stuck in a spiral, where cadence drops with fatigue, leading to increased resistance and force demands on your legs. This is sometimes called the ‘spiral of death’, and can result in you grinding to a complete halt.

It pays to be aware of these limitations when getting started with ERG mode so that you can use it to its full potential and get the best experience from using it in your training platform of choice.

When to use ERG mode?

ERG mode is suitable for most types of workouts, so if you enjoy riding with ERG mode, it’s good to use most of the time.

At the same time, it can be helpful to perform at least some of your interval workouts without ERG mode on. This will help you both assess whether your interval power targets are appropriate or might be holding you back too much, and develop some of those real-world skills mentioned above.

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From a practical perspective, ERG mode can be slow to adjust to changes in your target power, which can be problematic if you’re doing short intervals, and in this case riding without ERG may be best.

Top ERG mode tips

Finally, here are a few pointers to help you get the best from your rides and workouts using ERG mode.

  • Try to keep your cadence relatively steady, and if making cadence changes (e.g. moving from seated to standing), keep these gradual and controlled. This allows the resistance to adjust in line with cadence changes and will create less power variation
  • When approaching the start of an interval, gradually increase your cadence up to a comfortably high level. This gives room for cadence to drop as you fatigue without entering the ‘spiral of death’
  • Use the +/- function on your training platform to adjust your power target by 5 to 10% to accommodate how you feel on a given day