Insulin and Exercise, Part 2

It was beautiful outside this afternoon, and I felt a bit chagrined about not going for a ride or a run. But it’s my rest day, and the only thing worse than not going for a ride in beautiful weather is being injured and knowing that you can’t get back on the bike tomorrow.

And I did need the day off. I rode 60 miles on Saturday — I was rather amazed seeing how much flooding there still is out there — and then ran almost 9 miles yesterday. Even though I’d been telling myself all day that I was going to rest my legs, I didn’t really believe I would be able to resist getting back in the saddle until I bolused the full amount for my afternoon snack. That extra bit of insulin sealed the deal for me. I would probably have had hypoglycemia if I’d gone.

I think I’m finally getting a hold on how to balance exercise, food, and insulin. Everybody’s diabetes is different, of course — talk to your doctor, and don’t simply copy what I’m doing — but here’s what tends to work for me.

  • First off, active insulin really drives down blood glucose. On weekdays I exercise after work, so I usually have somewhere between one and two units of insulin on board; that usually guarantees a sizable drop that I have to compensate for with extra carbohydrates. But exercising first thing in the morning makes this moot. Of course, I do have to eat something first thing in the day, but I try to eat a small enough meal (<40g carbs) that I'm not going to send my blood glucose up a bunch without extra insulin. (Eventually, I'll figure out the right carb:insulin ratio for eating before exercise.)
  • During exercise, a couple of things happen that make insulin more efficient — as long as there’s some basal insulin present. More blood flow causes insulin to get to the cells where it’s used more quickly. (Remember, insulin is the metabolic “key” that moves glucose into certain kinds of cells, like muscles.) And the action of muscles expanding and contracting during exercise actually pumps glucose into cells with less insulin than when the muscles are at rest. So, I have to bring my basal insulin down a bunch (roughly 60-75% less than “normal”) about an hour before I head out.
  • Of course, just like people without diabetes, I have to get energy to my muscles; and that means eating. Over the four hours of my ride on Saturday, that translated into about 60g of fast-acting carbs (in the form of Gatorade) and 80g of more complex carbohydrates (Clif Bars . . . yum).
  • After exercise, it’s not quite like my type 1 diabetes is “cured” but I certainly don’t need as much insulin for my food. Exercise depletes muscle glycogen, which has to be replaced, drawing down blood glucose levels. I find that sometimes — but certainly not every time — I need to take off about 20-30% of my meal boluses, much less if I only go for an hour or so.

As always, I’ll keep fine-tuning and sharing what I know. What works for you?

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