My reply has to be taken in terms of heart rate and power.
This is topical for me as i have made myself a recumbent bike setup for my computer, idea to get 20 hour training weeks easily. And recumbent setup doesn’t provide nearly as high HR as cycling would so i was worried about it providing enough stress for me. As a avid cyclist with good aerobic base, able to hold 130 BPM (70% of HRmax) for hours, it seemed that under 110 BPM, 55% of HRmax, in recumbent setup would cause me nearly any stress.
I’ve been mainly on recumbent to test it out for, l only few times to get on bike to test my legs. Basically my legs are very tired from pedaling hours with 55% of HRmax. Yes, the setup is new to me so muscularily my body needs yet to learn economy so this isn’t apples to apples comparsion. But what i’ve gathered from this is that if it causes straining it’s enough to cause response. If my legs wouldn’t be tired enough from 4 hours on recumbent to affect my road bike the stress would be too low.
I don’t have power in recumbent so i can only estimate my power output, but i think i generally pedal around high Z1 low Z2 (z5 model). For my road bike that would be easy riding and i generally don’t do it but like to hover low-high Z2.
I’ve had this setup for 10 days, so i can’t provide long term observations. Only acute ones. But that’s the mental game with which i’ve come to terms with it:
tiredness = response. And from there on i try to estimate tiredness as a measure of sufficient response (=what is too low and what is not). Not because it’s optimal or correct, but that is all i have.
EDIT: I do physical job and do hold 80-90BPM in my work, however that isn’t enough straining for me to effect my training on bike… And it hasn’t baked me into pro level cyclist either. sadly. So i think i know when low is too low.
