I’m not a massive fan of ERG Mode in Zwift (and other indoor training platforms). There. I’ve said it! “WHAT?!” I hear you say? “ERG mode is the best! You can just have it set and not have to think!” And right there is exactly one of my points…. Now let me explain…..

Pretty much every athlete these days has a smart trainer for indoor bike sessions. A smart trainer is the ability of the trainer to be able to ‘talk’ to your computer / device / app and be able to control the bike’s resistance without the ‘need’ for you to change gears.

It then goes to the next step of having the ability to ride using ‘ERG mode’. And ERG mode is a setting in many training platforms such as Zwift and TrainerRoad whereas it fixes your power output to a specific target power in a structured workout and then automatically adjusts your resistance to match your cadence. If you don’t have ERG mode on, then you essentially have to generate the power / effort yourself – like the ‘good old days’! ;-p

Power is essentially calculated by how hard you are pressing on the pedals (torque) by how fast you are turning the pedals (cadence). So ERG mode uses these two measures to ensure you hit your prescribed power.

So if your session asks you to hold say, 200watts, the trainers resistance will automatically increase if your cadence drops (ie it will feel harder). On the flip side, it will decrease if your cadence increases – all with the aim of holding that 200watts.

When this feature first came out, everyone loved it. Oh to be able to jump on the bike, hit ‘start’ and simply ride without thinking too much. But lets think about that a little. Your riding without thinking? Without giving much focus on what you are doing – your pedal stroke, how hard you are pushing, what that ‘feels’ like – as long as you are able to ‘keep up’.

Now this CAN be great – especially for those who struggle to pace their efforts and regulate their power. It can also help you work through multiple intervals without being able to ‘slacken off’, or push for those last seconds / minutes when you may have previously given up sooner, or weren’t able to hold the power – think of it like a treadmill. Set a pace on the treadmill – you can’t slow down unless you manually change it. ERG mode does the same.

By having the power fixed to a specific target, ERG mode allows you to target specific training adaptions – ie if you are wanting to train in your threshold zone, or working on your VO2, and great if you are after a recovery or endurance ride and not go into that grey tempo zone…. ERG mode will make sure you are hitting those specific zones to stimulate the adaptions you / your coach is looking for.

To a lot of athletes, this can be GREAT! And don’t get me wrong, it can be, BUT there are also many reasons why I don’t love ERG mode……


  • ERG Mode is set on a specific percentage / target of FTP. Instead of a range. So when an athlete is aiming to target say VO2, ERG mode will force you to hold one defined power number. But this is not THE only number, there’s a range you can be in and still hit your target. So if you are ‘stuck’ in ERG mode, you could actually be putting a cap / ceiling on your training effort. Not ideal!
  • Your FTP can change based on the training load you are in, how recovered you are, the amount of fatigue you are carrying, etc etc. So some days your FTP will feel/be spot on, and others it may feel too hard or too easy. So some days, if you are in ERG mode an effort might feel too hard, and on others, it might be too low. Those athletes who have used training platforms such as zwift for awhile and know and understand this can adjust their bias / difficulty to reflect this, but an unseasoned athlete might just blindly follow along without understanding and adjusting accordingly…. And therefore not training as effectively as they could be. OR over train….
  • ERG mode can turn into a downward spiral if you start to fatigue / are fatigued and cadence drops below that comfortable range. The resistance will increase – like someone is tightening the screws, and this increases the feel of the effort for the same power. If you still can’t hold it, resistance continues to increase and your cadence will continue to drop . If you kept persisting, you may eventually not be able to turn the pedals! (for anyone who has done a ramp test on Zwift you will know what I mean!) ;-p This isn’t a space where you want to get to in a training session and should be avoided at all costs.
  • ERG mode has a ‘lag’ in the changes to your power targets. So if you doing a workout that calls for short sprint efforts, it can be an issue as it takes a few moments to bring the power up, and then the other end, takes a few moments to drop the power when your interval finishes! It will also mean short sprints won’t give the ‘feel’ of a true sprint – ie that big power spike as you take off, then the drop to the power you can maintain for the remainder of the sprint.. Not really gaining the biggest bang for your buck.
  • Athletes can get a little lazy and not even change gears on their bike while using ERG mode. Some could see this as a benefit, I certainly don’t! While we are using the trainer to increase our fitness and performance, we should still try and replicate the outdoors as much as possible – and this includes changing your gears. So if you’re not, then make sure you start.
  • I have also seen athletes who use ERG mode too much, loose their ability to be able to gauge their effort and pacing, being able to control power output with the appropriate gear selection and most efficient cadence and having the mental resilience to be able to push hard ‘on their own’ without being ‘forced’ to by ERG mode… Not ideal when you take your training and racing out on the road !
  • Depending on the session, the effort, and how you are feeling, sometimes ERG mode efforts can feel ‘artificial’. A way I describe this to my athletes is, it feels like your trainer/device is generating the power for you, and you don’t feel in control of the power yourself. You might be hitting the targets and the power and cadence but it just doesn’t feel like ‘real life’ riding. As if your fighting against the trainer a little to get the outcome, rather than being on top of it and riding smooth with great technique at the effort required. If you do this too often, bad habits can form…
  • I will often have athletes who love ERG mode, start with it on, but then during the session switch it off, and quite often they are actually able to push the same or MORE power with LESS effort. Go figure! And this comes back to that feel. When you generate the power yourself, you are nearly always going to get a much better feel than if you are pushing against the push/pull effort of ERG mode.

So – as much as there are some great aspects of using ERG mode and it certainly has a place in indoor training, I make sure my athletes aren’t using it ALL the time. I coach them to be able to know when it’s right / a good time to use it, when they may need to scale their bias/effort, or when they should switch it off and push the effort themselves.

SO – if you are using ERG mode often, I encourage you to switch it off every now and then, even within a session if you have repeat intervals, do one with ERG mode on, one with ERG mode off and see / feel the difference. Which one ‘feels’ more real life? And which one feels more artificially generated? And always go with the real life feel – even if it means your power is slightly lower….

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