3 Tips for Exercise and Type 1 Diabetes

When I daydream about a cure for type 1 diabetes (T1D), I dream about the potential of just going for a jog without much planning beyond making sure my AirPods are fully charged. With T1D, it’s so much more complicated.

But a little ol’ hobby of mine is making exercise with T1D simpler. The more you understand the science of exercise, the more likely you will actually enjoy your next workout.

Here are three things you need to know about exercise with T1D. (Find a deeper dive on these tips — and more — in my latest book, Exercise with Type 1 Diabetes on Amazon!) 

Learn the difference between aerobic and anaerobic exercise

Here’s the nutshell version: Aerobic (cardio) exercise tends to cause low blood sugar (hypoglycemia) because your body cycles oxygen to your cells where it burns glucose for fuel. The more insulin you have active in your system during aerobic exercise, the more likely you’ll experience hypoglycemia.

Anaerobic exercise, on the other hand, includes things like strength training, sprinting, and intense spinning intervals — and sometimes it spikes blood sugar levels. Anaerobic exercise is often defined as short intense bursts of exercise that you can only maintain for a couple of minutes at most. 

Your body is working so hard that it can’t actually use glucose in your cells for fuel because it can’t cycle oxygen to those cells quickly enough. Instead, your body produces its own source glucose by converting lactic acid into glucose and releasing glucose from the glycogen stores in your muscle tissue and liver. 

Your basal insulin definitely needs fine-tuning

Second, it’s all about that basal insulin! If you have too much basal insulin in your system before, during, and after exercising, you’re very likely gonna go low. But too often, I hear from people who say, “Well, I reduced my basal by 25 percent about 20 minutes before exercising! I still went low during … and 12 hours later!” 

Most people who say they plummet during a 15-minute walk are probably taking way too much basal insulin all day long, let alone during the dog walk. 

If you use a pump: a 20-minute temp basal with only a 25 percent reduction isn’t usually enough. Most people will likely need anywhere from 50 to 70 percent less basal insulin starting at least one hour before they begin aerobic exercise.

But the basal adjusting doesn’t stop there. If you’re going low in the hours after exercise, this tells you something very clearly: You’re still getting too much insulin. You might need to reduce your basal rate after exercise, too. And chances are, your basal rates are too high across the board. 

If you’re on multiple daily injections (MDI): There’s a good chance your total long-acting insulin dose is just too darn high if you’re going low when the only insulin active in your bloodstream during exercise is your basal insulin. You could be taking 5, 10, or 20 percent too much basal. 

Once you make that reduction, though, it not only applies to the day you exercise but potentially the next day, too. In an ideal world, you’d make exercise part of every day so this new basal dose works well for most days. The more consistent your exercise habits are, the more predictable the impact will be on your blood sugars and insulin needs!

It’s a careful balancing act — reducing your basal could mean you end up needing more mealtime insulin. The starting point though is to fine-tune your basal insulin so you can go for a walk (without any rapid-acting insulin on board) without hypoglycemia. If you go low, you may be using too much basal. 

Consider exercising before you eat

The moment you eat a meal, you’re adding several complicated variables to your blood sugar management during exercise. Variables like:

Deciding whether to reduce meal bolus by 10, 25, 50, 75 percent
How quickly or slowly that meal digests
Low carb vs. high carb quantity, which impacts insulin needs
The timing of the meal vs. when you plan to exercise — immediately after vs. one hour after eating, etc.
The length of your workout — anything over 1 hour might require refueling with more food

“Fasted” exercise is the act of exercising before a meal. In people with T1D, it also implies exercising when it’s been at least four hours since you took a full bolus of rapid-acting insulin for a meal or correction.

If you plan your exercise for when you are in a fasted state, you are eliminating several huge variables that lower or raise your blood sugar during exercise. 

For example, every morning before breakfast, I walk my dog 2.5 miles and run anywhere from 1.5 to 3 miles. My blood sugar does not drop because I haven’t taken any rapid-acting insulin for a meal. I’m on MDI and I’ve fine-tuned my long-acting insulin dose to ensure my blood sugar does not drop during exercise in a fasted state.

Look, there’s so much more to this! And I can teach it to you — but not in one article! Find my 100-page book — Exercise with Type 1 Diabetes — on Amazon!

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