ERG Training | 80/20 Endurance

ERG Training

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    I currently use Zwift for my indoor bike training. Should I keep the ERG on when I train the different zones or should I keep it off? Plusses and minuses?



    David Warden

    Tim, thank you for posting this question in our forums 😉

    In most smart trainers, Erg mode sets a static resistance, and the decides chooses that point within in the zone. For example, if your Zone 2 is sent from TP to the device as between 175 and 208, Erg mode will probably pick 192 watts as the static resistance (50% of the zone, or maybe 60, or 70%… depends on the device). No matter what you do, you will be pushing against 195 watts.

    In “free” mode, you are allowed to freely choose your effort. The risk is that you drift above or below Zone 2, but the truth is you have to learn to manage your intensity anyway, yes? You wont’ have Erg mode on race day!

    So, Erg mode is not evil, and maybe sometimes it’s not a bad idea to be forced to maintain a certain intensity. But, some days it is appropriate to train on the low end of Zone 3, and some days you can only gain new fitness if you are on the high end of Zone 3. Erg mode makes that important decision for you. For the most part, I think it’s best to learn to manage your own intensity.



    Howdy, this seemed like the best thread to bump with my similar question.

    I’m creating structured workouts in Rouvy from the plans in your fantastic 80/20 book. Thanks!

    Given my current indoor setup, ERG mode is my only option, and I strongly prefer to use it. I’m an experienced cyclist and get plenty of pacing and intensity management outside. ERG mode helps me get more volume inside through the winter as I can watch movies and do other mindless stuff without thinking about the workout, just maintaining 90 rpm.

    I’ve been picking the middle of the zones as the default target, so 60% of FTP for Z1, 76% for Z2, 95% for Z3, and 106% for Z4.

    Are these reasonable values to use as defaults? I can adjust the power (% of FTP) up and down during the workout as I feel necessary, so no worry about getting stuck at the value. (The same can be done in TrainerRoad, but not sure about Zwift.)

    However, psychology is that I always tend to stick with the power I’ve programmed for the workout. So I’m wondering, in general, if the target % of FTP is better to be in the high, middle, or bottom of each zone?

    David Warden

    Anthony, great question!

    It depends on the zone. Zone penetration for easy (Zone 1-2) should be setup to allow for sufficient recovery. If you are coming off of a tough workout the day before, then low Zone 2 is best. If you are coming off of an easy day or after a rest day, maybe high Zone 2. With Zone 1, I aim for the high end for warmups, but the low end for recovery intervals. There’s a lot of “art” in deciding how hard to push Zone 1 and 2. When in doubt, go easier.

    For high intensity, the decision is much easier: intensity should be the highest possible zone penetration can consistently maintain for the workout or interval. You don’t want to be bouncing all over the zone. Pick the maximum intensity you can maintain. If that’s 25% penetration into Zone 4, then 25% for every interval that’s better than 95, 40, 20 and 50%. For a long Zone 3 interval, you should be holding steady for 8 minutes, not fading from 265 to 259 to 255.

    Regardless, your mid-level target for each zone is great, it gives you the flexibility to easily pick the sweet spot for that particular workout.



    Thanks for the fantastic answer, David! Very helpful.

    It will be great for me to start thinking of the zones as a range rather than a number and learning to improve at picking the best spot in the range in the context of the workout and how I feel. Thanks again.


    Hi there all.

    New to this training so newby question that relates potentially to ERG mode use. When I use the linked training (from Trainingpeaks) plan on a ride day with the online program (fulgaz) I have it sets the power in the middle of the zone 1/2/3 etc. However my resulting HR runs at least 1 zone higher than required. Hence I’ve artificially dropped the FTP to lower the HR.

    Reading above and another thread it may be best to also stop using ERG mode and ride at the lower end of the recommended power for any zone. Am I understanding this correctly?

    Also if I still seem to be riding at a higher HR than suggested I assume HR is more important therefore I should ride following that rather than the power metric. Is this also correct?

    David Warden


    Lot’s of great issues included in your question:

    – Your Power and HR zones will only line up if you test both Power and HR thresholds at the same time. If they are tested separately, they are unlikely to line up. So, this issue could be resolved by testing them both during your rest week.

    – Even if you do perform the HR and Power tests at the same time, they still may not line up. HR will change for a given power based on all sorts of environmental factors. That’s why Power is the gold standard of training: it is consistent (see our automobile in our document Intensity Guidelines for Triathlon).

    – HR is not more important than power. In fact, I’d consider ignoring HR altogether and only focusing on power. Try taking off the HR monitor for a couple of weeks and you may never go back.



    Ok then. Since I’ve both cycling and running power meters then once I’ve done a FTP test then I should use those metrics not the HR ones.

    That may result in higher HR readings however the resultant power zones will result in a better long term training/fitness outcome. Correct?

    David Warden

    Yes, but don’t give up on aligning your HR and Power zones. It’s still possible if you perform the test and capture both HR and Power within the same test. Especially indoors, where the environmental factors are more stable. But, if they don’t align some days, that’s OK. That’s normal with HR.

    However, in general, your training will be more effective and consistent, and your zones more accurate with Power instead of HR.


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