"I'm less clear on whether it's likely that someone doing a two-week backpacking trip of, say, 15-20 miles a day will have any realistic chance of breaking down muscle … but I'm prepared to be educated :-)"
I had it happen to me, Ben. Ever since, I've referred to myself as "self educated". It was an unpleasant enough experience that I did the reading necessary to find out why.
While you've got the McArdle book, look up gluconeogenesis. Also, Wikipedia has an excellent short description of it, as well as the conditions that trigger it, one of which is a low carb diet/glycogen depletion situation. Let the education begin. ;}
