Aren't you the exercise physiologist? If you're not doing anything too stupid with your fueling strategy, it's likely fatigue cramps. Basically, your neuromuscular system gets tired and stops functioning correctly, and then tries to catch up the contraction all at once with one awesome glorious drop-you-to-the-ground-writhing cramp. Yay. Here's
a non-scientific article that goes more into depth.
Nice run, though, sorry it ended in a slog.
Well, I have a Physical Education degree, I wouldn't necessarily claim to be an exercise physiologist.
Sure, cramping due to fatigue makes sense. I would say that I could really only figure that if I thought that my fueling was optimal, and I suppose I don't think it really was. I think more fuel and drinking at every aid station would have helped more. Regardless of what Noakes' book said, I feel like going fully experiential and comparing my experiences with electrolyte supplementation and no electrolyte supplementatiom is all the evidence I need.
I managed to escape the full on cramps. Rather, it was a lot of close call twinges, especially when requiring that little extra power burst to not fall over.
Though like I said, my calves, being compressed to the gills, were pretty good the whole way through. The same lack of efficacy studies can be found about compression, too.