Indoor Training

Currently, the weather in the northern hemisphere is pretty cold, there’s a worldwide pandemic and many of us are inside riding the indoor trainer. Currently, due to these points and a few others I’ve been riding solely indoors since November, and this has given me plenty of time to ponder: should you do your indoor training (at least for structured workouts) in erg mode, or should you ride in ‘simulation’ mode?

I do the majority of my riding on the Zwift platform, using my Tacx Neo. If you haven’t used it before, ‘erg’ mode (short for ergometer mode) allows you to ride at a predetermined power output no matter how hard or fast you pedal. If you create a workout such as 10-minutes at 200 W, and 2-minutes at 300 W and 10-minutes at 150 W, Zwift and the indoor trainer will communicate with each other and no matter what the scenery is showing in Zwift (e.g., a level road, and uphill, or a downhill) you’ll be forced to ride at 200, 300, or 150 W (or whatever you set the workout to be). If you ride at 20 revs/min or 200 revs/min Zwift will keep you there at that required power output.

Conversely, you could memorise the session and using ‘slope/simulation’ mode you’ll have to manually alter your pedalling cadence and force to ride at the requirements of your session (just like you would if you were outdoors).

So, which, if any option is the better one? Last week I started some new intervals, which were 2 sets of 30-seconds on and 30-seconds off. I felt that this would be a great session to do in erg mode. I wouldn’t have to bother about changing gear, or cadence; all I’d have to do is just keep the pedals turning and the Tacx and Zwift would do the rest.

I started my warm up in erg mode. I was pedalling away at my usual 90+ cadence, but even this felt weird when riding at a low power. It felt like a brake was constantly being applied to my Neo and my cadence would start to decrease, which in turn increased the braking force more and made me want to slow down. It was a really strange sensation. Lots of people call it the ‘spiral of death’ because when you start getting tired your cadence drops, resulting in the trainer increasing the resistance to maintain the same power. As the resistance goes up, you naturally slow your cadence again, meaning the trainer once again increases resistance… and so on. Whilst you can try to increase your cadence to reduce the corresponding resistance, this requires additional effort and concentration. It’s an odd experience.

Just prior to the actual interval block starting I switched out of erg mode and continued in simulation mode. It felt way better, and I completed the first set of intervals. Once the first set was done I had a long period before the second set started and switched back to erg mode. I didn’t like the feeling, however I persevered. I then completed the second set of intervals (they were the same as the first set) in erg mode. It was grim riding but I did it! I then cooled down in erg mode.

After the session I analysed my data. Interval set 1 in non-erg mode had slightly higher power for the ‘on’ periods (1.3W higher) as the erg mode interval set 2. The recovery power in non-erg mode was higher than in erg mode. This resulted in a higher average power in non-erg mode by 11W and a higher normalised power by 5W. However, riding in erg mode felt awful.

As with most things in life, everyone has a preference, and when I asked other riders there was a mixed response. Some riders preferred erg mode (even on the same indoor trainer), while others hated it for the same session.

Having also used erg mode on other indoor trainers the feeling is different, and for me it felt ok on a Wahoo Kickr. Consequently, it’s probably worth changing things if you’re struggling with a session.

Don’t be afraid to experiment with how you feel and respond to your equipment and the intervals you’re doing. For certain, it feels like highly structured intervals should be done in erg mode to reduce complexity, but for many it feels easier and much more doable when you ride in non-erg mode. And, if you can do more of a session, or ride at a higher power in one setting rather than the other, then that’s what you should do.