Hi Emma .I've had a similar problem, and my weight/ total insulin on MDI was similar to yours.
I partially solved it on MDI (enough to do a marathon) but to be honest it is now far easier on a pump because I can turn my basal down to a dribble during exercise and at times I suspend it entirely. I seem to need very little insulin for exercise, but need 'normal' amounts whilst sedentary The trouble with a long term insulin is that you can't switch it off. Your doctors idea of cutting basal on exercise days was also suggested to me but it does depend upon a certain amount of preplanning and I was never that organised.
What I did on MDI was to test frequently, before. during and after exercise and experiment with different types of carbs and bgl . I tried starting at different levels, eating long acting carbs before etc etc
From testing I discovered that my levels dropped drastically during the first 20-30min (interestingly the Runsweet site confirms this as a 'normal' phenomena). I found that it didn't matter how high my blood sugar was before, it still fell to a hypo level so it was useless making levels artificially high. I did/do reduce the bolus by a unit or so with the meal before but not drastically.
After about the first 20 mins I took a couple of dextrose tablets I was then OK for another 20- 30 minutes when I'd take some more dextrose, normally only 1 tablet. I never need much to lift my levels. (1 dextrose tab has 4gms carbs)
On longer runs after the first hour or so my levels took longer to drop so I didn't need to take dextrose quite as frequently. When doing the very long runs in training and the marathon I would drink a 'sports' drink during the later stages.'
It worked, I was able to complete the runs but I'm not fast and not competitive, I think thatwho people want to be competitive need a very different type of strategy. (ie they need to keep their levels higher all the time)
I find that I often go low about 5-6 hours after exercise so reduce the bolus of the meal following exercise. I have read advice that taking a small snack of mixed protein and carb immediately following exercise can help prevent this later drop. Its something I haven't, but should try.
As I said, it worked but not as well as being able to cut my basal with a pump, I was able to go for an all day bike ride recently with no hypos, no regular dextrose tabs and only a normal picnic lunch
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