Often times I come from work very exhausted, unable to do anything, including having a dinner, which my body needs, I think. If I reluctantly stuff some food into me and cycle for an hour or to, I become so invigorated that I seem to be able to keep going on and on: cycling, or coding - I can do it. The prudent thing here is have a proper dinner and sleep, I guess.
I was told that "marathoners go by the pulse meter" (i.e. not odometer/speedometer), I wonder how true is this for marathoners and for endurance cyclists. Maybe at the point in your training where you have personal trainer and follow car, you don't need pulse meter that much? I am never going to be there and I have high hopes for training with pulse meter.
Here's an obligatory video introduction to racing cycling culture:
MC SpandX "Perfomance"