It really varies on how well-conditioned you are, as to how much of a sprint you would need to raise your BG. You can definitely raise it, if you do it hard enough and for enough duration.
The best thing to look at is heart rate and duration at that elevated heart rate, not speed. Because speed will vary based on how tired you are.
I know exactly what heart rate will spike me, and how much. It’s useful to know.
I have discussed this many times on the site. Here is a link that kinda explains it.
exercise-predicting-blood-sugar-bg-changes-up-or-down
Basically, at high intensity levels, the spike is just the body’s natural response. It’s a typical “fight or flight” response.
If you are being chased by a tiger, your body would want to make sure it does everything it needs to escape. So your body releases hormones - epinephrine (adrenaline), norepinephrine, and cortisol. Your heart rate and blood pressure increases. The oxygen that goes to your tissues increases. And your liver releases glycogen stores to give your body fuel.
Everything that is happening with high-intensity runs is the same as it would be for a non-diabetic. The only difference is that the non-diabetic doesn’t see their blood sugar spike because their pancreas automatically releases insulin for the extra fuel from their liver glycogen.
And it might not really be a fast run that does it. You might have a significant increase in your pace:heart rate ratio on a long slow run, if your pace is greater than your fitness level.
For example, if a 10 minute pace is tough for you, you might not spike after 1 or 2 miles at that pace, but after 5 miles your heart rate will have increased a lot more than it was early in the run. And that might be enough to do it. So it might not seem like a “fast” run, but the heart rate increase over the length of the run is enough to cause an eventual spike.
Also, it might be that this whole conversation is not even relevant - maybe it is because they are turning off their pump for the whole run, or taking a bunch of sugar before hand, and that is causing the spike.
All of that is to say, that’s why short little pre-canned answers may not be what your friend needs. It takes a little bit of back-and-forth with someone to really give them the best answer that applies to them.
So you can give them canned answers, but the best answer for them will be after an exchange of info.