I've switched to a polarised training regime this year. So 80% low intensity, 20% high intensity and nothing in between. The difficulty of using ERG mode is finding the right intensity to push you into the right territory. Low intensity I do outdoors as I couldn't face hours on the turbo.
I've been using 30 / 15 intervals. So 30 seconds high intensity and 15 seconds recovery. I'm currently up to three sets of 10 X 30/15 per session. I started at 90% of my maximal aerobic power (highest 1 min power during a ramp test) a few weeks back. Today I set the intensity at 105% of MAP. It meant I hit 94-98% of my max HR during each set with 15 seconds recovery not enough for HR to drop much due to lag. So it was close to 30 mins accumulated at 94-98% max HR. Interestingly my HR was still climbing slightly during last set so wonder if I might be able to eek out a few more beats to a new max HR in a few weeks.
How hard was today's session? Well I had to close my eyes during the intervals as even looking at a 30 second countdown would have been too much. Even looking with 10 seconds left I was desperate for it to end. Then the 15 second recoveries flew by.
Hard is what I wanted, hard is what I got.
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@HLaB I wonder about not doing this in erg mode and just going as hard as I can to find the right intensity level during any one workout.