3-4 hours. I may add some 5-6 hr rides once a month, (approaching century), but I generally find them too boring. My observations come a little more from gym work-outs that tend to be more..dynamic. I warm up running a 5k, then do a BOSU work-out or drop into a class, like kick-boxing or spin.

I don't think you're right about "the glycogen reserves are stunning". I think exactly the opposite is happening.

Maybe, I don't know that answer for sure & I have an open mind. But I have been reading about training and diet greatly impacting glycogen reserves, like 1000% improvement, and my subjective experience seems to bear that out. I say that because pretty much all the peak and valleys are gone, daily energy is constant state morning afternoon & night. Eating in the evening doesn't much change anything, working out in the morning or evening isn't much different. If you are correct, then I would expect to experience a glycogen bounce after the 6pm meal, feel like pounding it out late night, early morning. Never happens. Occasionally I'll fuel with a Cytomax drink before a tough gym workout, but that doesn't seem to make much difference either. The most empirical explanation seems to be: glycogen is on a meter, no peaks, no valleys.

I'd be interested in the references, because nothing I have ever read suggests that is possible. What I understand to be possible is using those glycogen reserves much more slowly, by becoming more efficient at fat-burning. That would be consistent with your endurance improving.

Well, I'm not sure if it was intermittent fasting medical journal articles or Ori Hofmekler's book "Warrior Diet". Seems like something Ori would say, I'll take a look this weekend if I find a quote and I'll pass it along.

The other reality is IF-ing make you a little blase about your workout. I've been known to yawn during a "hi intensity" workout, more interested in girls walking by then blasting out a set or aggressively spinning up a climb. That might be consistent with your statement that it's a low octane fuel you're burning.

Fail. Can't find this reference. Ori's book talks about "Glycogen Stretching", loading and depleting to to increase storage in muscles through adaptation, improving the liver's capacity to convert lactic acid to energy..which is statement that loosely tracks along the lines of this article https://www.sciencedaily.com/releases...0420235214.htm. And this article talks about stabalizing serum levels: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC156352/

Well, I read it somewhere...