How fast before your insulin kicks in?

You might want to get the book Using Insulin by John Walsh, Stephanie. It explains so many of the little details that many doctors either don't know or don't have the time to go over (like ISF)

Your doctor may give you a number or a formula, but really the only way to figure out your ISF is by trial and error since we are all different. When it's moderately high, take one unit of insulin and see how far it brings your blood sugar down in three hours. Do this regularly and write down the results, starting conservative and raising or lowering the number as indicated. Also it may be different for different times of day; mine for example is 30 during the day but 60 at night. (One unit drops me 30 points during the day but 60 points at night).

Well, 21.2 mmol/l translates to 378 mg/dl. In Germany we have the rule to have no sports above 250 mg/dl. For these high numbers you will inject massive amounts of insulin. To combine this with additional physical activity can lead to severe lows. The high glucose can be the sign of having a huge deficit in insulin coverage. In this case the body might have already changed its energy source from carbs to fatty deposits. As a result high levels of ketones from burning the fat might be flooding your blood stream. With ketones it can be really dangerous to get physically more active (risk of DKA). In this situation you will need much more insulin because the insulin sensitivity will be greately reduced. You also need to drink more to flush the ketones out of your system. Another point is that some physical activities might trigger the muscles to release their glucagon stores. This can further increase the blood glucose. In this situation one variable - the insulin - will be enough to control. Inject, test often, drink and bring it down safely.

I do not exercise strenuoulsy over 250. I do what Holger suggests: Drink a lot of water, inject with Apidra once, then closely, for 3 hours;Monitor the blood glucose. I may have to do a correction through the pump about 3 hours later to get it to the 100 -120 range I like in order to eat a meal or snack. I will exercise and correct if under 230 or so, but not strenuously Just light house work or a brief stroll around the block.

re the correction using severe lows business, I use the "exerchart" from "Think Like a Pancreas" as the basis for the correction, taking a %age of the bolus based on duration and intensity of the exercise, usually "moderate" for me. So if I'm at 300 and the pump says say 2.5U, if I were to exercise for 30 minutes at moderate intensity, I'd take .67 of my calculated bolus and then exercise it down. I haven't ever had DKA and sort of think that is more likely to result from prolonged hyperglycemia than an "oops, maybe that was more carbs than I thought..." I also find the fact that I'm engaged in an activity that will push my BG down makes me feel good and all of that but I may be a weirdo about stuff like that. The CGM pic on my page here @ Tu is from the Chicago Marathon, pretty much starting w/ the end of night and showing the boluses during the race.

I have a pic of the "exerchart". I know it's online but haven't been able to find it.