Doing The Omnium today, on the Pursuit interval my legs were dead with 2 minutes left and I switched from ERG to Level 2 mode, taking about 11 seconds to do so. Once in Level mode, I had no trouble sustaining a power level 15-30 watts more than the target to finish the interval then switched back to ERG and finished with my best IF and NP for this workout.
I’ve encountered the phenomenon before of being able to maintain or exceed a power level in Level mode that I couldn’t hold in ERG. Does anyone know the physiological explanation for this? My trainer is a Kickr Core.
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I think the erg mode is pretty challenging on high intensity, and when you fatigue and lower your cadence, it just makes up for that with more resistance which is unnatural. Then you fail. Whereas with level, the power output rises with cadence, and if you need a few seconds or a minute to recover on level mode you can get that and then return to intensity.
Kickr core twin here. 
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Yes I find the same. I’ve started doing 9H and AVDP etc in level mode now. I think it’s because ERG is effectively pulling you back, whereas in level mode you’re pushing forward, if that makes sense. Bit like simulating running up a hill by someone by someone pulling you back.
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Here is the dilema, with ERG the ‘smart’ trainer has to maintain the watts at a defined level. To do that it has to look at what the Watts are now can combine that with your cadence to work out what the resistance should be to either keep the same watts, increase it or decreate the watts to hit the desired target. The bigger the increase or decrease e.g. currently 150 watts trying to get to 300 watts with the same cadence means ramping up the resistance a lot quite quickly, this generally reduces the candence while you feel the resistance and then pedal harder to keep the same cadence at which point the trainer can overshoot the target and you find you are doing more watts that expected and the trainer is then trying to reduce the watts to hit the target and the cycle continues. Some trainers are better at adjustiung to these changes than others and a lot comes down to personal choice on how quickly resistance ramps up / down. With level mode all of that goes away because the resistance is fixed rather than constantly changing to hit a watt target. Personally I find that shorter intervals of less than 30 seconds work best with level mode and longer than that work best with ERG but it takes some experimentation and changes every time you change trainer 
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The best way I found to overcome this is to play around with the gears on the bike. I found that my cadence is normally quite slow so if I have to hit and maintain a high value with a high cadence I generally struggle on ERG mode so I tend to decrease the resistance of the bike / gears to increase my legs speed for a bit.
With that being said, I have quite a big gear on the bike 
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The most common thing that I have seen affecting this is the changes in resistance in Erg mode happening “too quickly.” You can ramp up the resistance yourself in level mode, giving you the opportunity to get there without crushing your legs. Erg mode doesn’t have that option.
There are a couple of things to try, especially with efforts where you go into the AC and NM zones of a workout.
- Choose a larger gear on your bike. This keeps the flywheel spinning more quickly which evens out the changes in resistance a bit.
- Ramp up your cadence just before the interval starts. This is the real trick. When you have a big interval coming up, start increasing your cadence in order to increase the flywheel speed of the trainer. This will help prevent the resistance from burying you at the beginning of the interval.
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Thanks Cody. I had not considered the physical dynamic factor of the flywheel because in Erg, the resistance is the same no matter what cog you’re using but it makes sense to take advantage of the inertia created by spinning the flywheel faster. When riding outdoors, increase my cadence on before starting a climb for the reasons you stated so it makes sense to do it on the trainer as well.
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