Champ, you're looking at very small pieces and interpretation of old data. Yes, carbohydrates are limited. But, again, the 45 min window is arbitrary dependent on intensity. I'm not arguing with 45 min per pitch being a rule of thumb in planning pitches and think its a fair number. But substrate utilization is dependent on intensity. Duration plays in to it and cause also cause a shift in usage too. And again, new data suggests that it is not just substrate availability that leads to fatigue. They've hooked people up to glucose infusions and they still crack. And yes, plasma glucose has a major contributor from the liver, but its not as simple as you state where you use all your muscle glycogen and then move on to the liver. Instead, your liver is pushing out glucose all the time dependent on intensity just as your adipose tissue pushes out triglycerides for energy use. Plus, oral intake contributes significantly. That bar you eat at the belay adds quite a kick if you get enough carbohydrates in it. And besides, the big thing we have BOTH failed to hit is that intramuscular substrate doesn't mean squat if fuel is the limiter--its blood glucose levels crashing that leads to a bonk. The only thing your body cares about regarding fuel is keeping your brain fed first. Your muscles are just sucking down energy. I used to have some awesome graphs explaining substrate, time and intensity that I used when I taught exercise physiology. If I can find them, I'll post them as they make it easier to grasp all the variables rather than a bunch of typing.
As far as your other post, again, you have stuff that is correct, and things not so much. Yes can can train muscle fibers to act like other fibers. But, they only act that way. Muscle fiber composition is genetically predetermined. But training can make muscles act "slower" with adaptations. You get alterations in enzymes, increased capillary density, increased mitochandria, and changes in substrate store intramuscularly. That slow twitch fiber, though, will always be slow twitch as determined by the inervation. If you did the ol' swaparoo with the nerves, then you'd see a change in characteristics. And pH as you mentioned changes a lot of things. As does heat, hormones, and items we're still trying to explain.
Oh yeah, I studied in Coyle's lab for a bit and had him as an instructor for several classes. Regardless of what people think of the man, he was willing to always point out that we have the tendency to take a data set and incorrectly apply it universally.
Thanks for the props old school. I do have a bit of history in the field. I train endurance athletes as well as taught this stuff before moving north and becoming a murse. Its dorky, but I enjoy teaching and guess that leads to online ramblings when I'm couch-bound.