If you're not training for an event/race and are using tr to supplement/replace/complement "just riding bikes" then over unders and interval sessions are probably going to be a right ball ache.
It helps if you get a kick of excitement and adrenaline before each interval.
I find that my HR and breathing rate increases shortly before hard intervals, which is take as a good sign that I’ll make it through the intervals.
If it doesn’t, my body has given up, and I am in for serious punishment.
If you're not training for an event/race and are using tr to supplement/replace/complement "just riding bikes" then over unders and interval sessions are probably going to be a right ball ache.