I have been on keto since the beginning of Dec and recently took up the cycling. The first time I went I managed to fall off (don’t ask!) and it took a couple of minutes before my legs had enough strength to lever me back to my feet! Second time, l completely ran out of fuel while attempting to pedal up a tiny incline - not breath, but muscle energy. “Bonking”, I believe cyclists call it!
This was a tad concerning as you can imagine. However, I have managed to overcome this - I am no expert on the metabolic process but it seemed to me that my body might need a little more time to mobilise the fat stores rather than using the carbs which used to be freely swimming around in my bloodstream. I also believe that water is critical for a lot of metabolic processes. So now I make sure I am hydrated before I start and keep hydrated even on a little local bike pootle. And I also make sure I have warmed up with some gradually increasing effort before asking my legs to take me up something really challenging like a short, gentle incline...
Anyway, upshot is, provided I do these two things I don’t have any issues. I don’t need to eat before exercise, not even for an early morning outing, nor am I starving afterwards. Just wondering if this approach might also help you?