I hear all the time how we can deplete glycogen. I haven't seen one paper to support it. Maybe I missed it? Or maybe we can only deplete glycogen when we are running on glucose, i.e. a high carb diet? How would this work when we're running on fat?

The way I understand it, when we're running on fat, blood glucose doesn't serve as a fuel. Rather, it works as a kind of additive, like nitrous oxide for a gasoline engine. Or maybe like a primer as in a water pump (in order to pump water, we must first fill the first immediate pipe surrounding the impeller with water, otherwise the pump is spinning in free air). Except, of course, in those cells that require glucose due to their lack of mitochondria. Then, glucose is used as fuel. Even then, some can use ketones to replace some, or all, of the glucose that would otherwise power them.

The point is, there is so little need, or even actual use, of glucose that I doubt glycogen will ever be depleted, if at all, when we don't eat carbohydrate.

On the other hand, the whole thing about insulin sensitivity, LPL activity and fatty acids uptake during exercise, I can understand and I could probably agree with it.

On the third hand, if it works, it doesn't matter how, does it.