Yes I see this every time I exercise (prediabetic, at least as measured by HBA1C; by other measures dunno). It's 'normal' for this to happen, even to 'normal' people, based on the adrenaline/glucagon response, but it happens to a greater extent (it seems) to people further along the IGT spectrum. I am guessing because the glucagon still functions but the insulin control of that resulting dump of hepatic glucose doesn't work as well.
I can find pretty much nothing about this effect anywhere in the diabetes forums or NHS guidance, so I have been chatting to the Super Sapiens people. These guys have some smart looking software along with the libre sensors to try to optimise fuelling for endurance sport. They are also by and large 'normal'. Some of them see spikes up to 10 or so when doing some hard exercise. Defining 'hard' is somewhat tricky, it depends on your fitness level and typical exercise regime. It seems to be related to how stressful the exercise is, so for me spending an hour at fairly high intensity (threshold HR) on the bike can spike me to 13. Weirdly maintaining the same HR running never gets as high.
I usually exercise in the morning and depending on the strength of the dawn effect that day can go from 5.5 overnight to 13 without any food ever passing my lips.
