I have type 1 diabetes and run about every other day, about 5 miles during the week and longer runs, 7-10 miles, during the weekends.
A good BG level depends on what time of day I am running, and if I have any lispro in my system. (I take lantus at night - 16 units - and dose with lispro when I eat). .
If I run in the morning, with no lispro, then I like to have a BG level of around 100-120 for 4-5 mile runs. I actually find my BS levels go up when I run this distance. I usually don't eat before I run, but have a cup of coffee.
If I run before lunch, I like to wait for atleast 5 hours after taking my morning lantus before I run. During these runs I like to get my Blood sugars up to around 170 or higher before I run. At the end of my runs my blood sugars tend to be about 90-100. It appears that the lantus is still active in my system, even though I usually only dose 4-5 units of lantus with breakfast in the morning. (Temperature appears to impact BS levels, the warmer it is, the lower my BS levels go during my runs.)
I always run with sugar tablets. And if my blood sugars were lower than I would have liked at the beginning of the run, or if I run within 4 hours of a shot of lantus, then I typically will c heck my blood sugar about 30 minutes into the run, and treat accordingly.
Elena, as I am sure you know, everyone is different, so your best bet is to experiment and see how your body reacts.
Hope this was helpful,