The On Board Issue…
I’m proud to say I’ve managed to adhere to my goal of exercising before work instead of after for almost two full months now, and I’m finally getting pretty used to it. And although morning workouts have a whole slough of unique diabetes issues to them, there’s one they generally don’t have: dealing with insulin on board.
When I workout first thing in the morning, it’s usually on a close-to-empty stomach, save for a coffee or cappuccino (then I eat within about 30 minutes of end of my workout), so I don’t usually have any bolus units on board except to treat an occasional morning high. I haven’t had to think about how many hours it’s been since my last rapid-acting insulin dose recently. Yesterday though, due to some logistical issues with my current week from hell busy schedule, I was forced to workout in the late afternoon, and realized that although my BG was 175 pre-run, I had taken my last bolus at 1pm for lunch, and it was still lingering around in my bloodstream.
Insulin on board, or IOB, is truly one of the trickiest things about insulin therapy, because it’s not exact but it can really screw things up if you’re not planning for it. Most doctors and CDEs will tell you that rapid-acting insulin hangs out in your body for about four hours, and that you can roughly calculate the amount you of insulin you have on board by slicing it in fourths. For example, if you took eight units of insulin for lunch at noon, you would have six units on board at 1pm, four units at 2pm, and so on until its “all gone” at 4pm. The trouble is, insulin is never really that predictable - at least not in my experience, and all of this can completely change depending on what your blood sugar was when you dosed and what you ate.
It’s a rough calculation at best, but I do know that if I personally have any IOB during exercise, I’m likely to plummet like a rock in a river during a workout. I get hit so hard in fact,that I really try to avoid exercise in the four hour bolus window if at all possible - even a brisk walk can send me dropping. But just like everything else with diabetes, life makes it really hard to adhere to these time blocks. There’s been plenty of times where I’ve wanted to squeeze in a workout at a random time during the day only to realize I’m 95mg/dL with IOB. That won’t work for me.
As I get more into my training for the half marathon, I’ll be back struggling with my old friend IOB, as I know I won’t be able to do some of the longer, two-hour plus runs before work (look people, I’ll get up early to workout but not THAT early!). And just like everything else with diabetes, it will take a little extra planning, a few mistakes, and the energy to try again.
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Comments
Amen - as someone who likes to ride 50 miles on weekend mornings I know how hard it can be to get boluses and temp basal right. One thing you might find is that doing a longer run without eating first is nigh impossible. Once I broke into the hour and a half or longer rides I found I needed the extra carbs from breakfast or I just ran out of energy. You might try reading ”
Diabetic Athlete’s Handbook” by Sheri Colbert, PhD. My CDE recommended it to me and there’s lots of good information about what works for other diabetic athletes out there.
Good for you. Distance running like that takes lots of practice - I still haven’t figured it all out. It’s worth it though so chalk up the roller coaster runs as experience and pat yourself on the back when the diabetes gods are with you.