In just the past few years, diabetes technology has come a long way. In 2016, the first hybrid closed-loop (HCL) system, produced by Medtronic, received approval from the U.S. Food and Drug Administration (FDA). Since then, manufacturers Tandem and Insulet have also gotten FDA approval on their HCL systems. But despite the availability of this cutting-edge technology, techniques for using it to achieve optimal glucose management during sport are rarely taught to those with diabetes, creating a barrier to exercise for many people.
Physical activity offers a long list of benefits, both physically and mentally, so it’s important that people with diabetes can safely participate in the activities of their choosing. If you’re using an HCL device, there are some strategies that can help.
What is a hybrid closed-loop (HCL) system?
In a nutshell, a hybrid closed-loop system is an insulin pump that communicates with a continuous glucose monitor (CGM) to automatically adjust insulin dosing (via either temporary basal/background adjustments or automatic bolus dosing) to help blood glucose stay within a person’s target glucose range. All of the systems on the market — Medtronic’s MiniMed 770G, Tandem’s Control-IQ with Dexcom G6, and Insulet’s Omnipod 5 — function in a fundamentally similar way but with a variety of differences. Someone interested in using an HCL system should be educated on the specific features and functionalities of each of the commercially available devices to help them decide what would work best for them.
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Because each system will automatically lower or turn off basal insulin delivery when the glucose level is predicted to drop below target, many people think that adjustments are no longer needed for physical activity when using these devices. Others think that simply setting the system to its pre-programmed mode for physical activity will do the trick. However, this is typically not the case. That’s because systems cannot tell exactly what you plan to do in the future — for some activities, the device still needs additional information ahead of time.
Unfortunately, the current guidelines for managing glucose during exercise focus primarily on people who use multiple daily injections or traditional (open-loop) insulin pump therapy. Because HCL systems work differently, they require a different approach to diabetes management during physical activity. Some of these approaches have yet to be standardized, but there are a variety of principles that can help.
Techniques for exercising with an HCL system
For exercise that tends to lower blood sugar (most types of aerobic/cardiovascular physical activity), here are some strategies that can help you manage your glucose with your HCL system:
• Increase your blood glucose target (or engage the system’s activity mode) one to two hours prior to engaging in physical activity. (This must be done in advance due to action time of insulin — if the basal insulin delivery is not adjusted until the activity starts, it won’t have an impact until it is too late.)
• Consider the glycemic index (how quickly a food causes blood glucose to rise) of any carbohydrates you have consumed and the fact that digestion slows down during exercise. Keep this information in mind to avoid having insulin on board that is peaking while digestion is slowed or increases in basal or bolus insulin delivery during exercise. (For example, someone using an HCL system who delivers a bolus for a moderate-glycemic-index food eaten prior to exercise will be going into the workout with the food not yet digested and fully impacting their glucose levels. Additionally, the insulin may be peaking during the workout, and their insulin sensitivity will be increased due to the exercise, so they will most likely end up with a low. Following the activity, they may then be more likely to see a rebound high as the food begins to digest again.)
• Try to avoid rapid rises in blood glucose just prior to exercise.
• Take into consideration what the system is doing in the background and know that less carbohydrate may be needed to maintain your glucose level than what was required before you were using an HCL.
• Be aware that if a meal is being consumed one to three hours prior to exercise, a decrease in the amount of insulin to cover the food is typically warranted due to the glucose-lowering effects of the physical activity.
Each HCL system allows for different automated glucose targets or “temporary presets” to be set in advance of exercise. These targets set prior to exercise are typically higher than standard target glucose levels — this helps prevent the system from giving too much insulin, since physical activity typically increases insulin sensitivity, and administering the usual amount of insulin could lead to hypoglycemia (low blood glucose). Depending on the system, the target blood glucose for exercise is often set for a duration of time, automatically returning to the usual glucose target after the preset duration. (With Tandem’s Control-IQ technology, the user needs to remember to manually exit activity mode.)
It’s best to talk to your health care provider about what target is best for you if you use a system that is customizable. On my own HCL device, I use an exercise target of 140 mg/dl. Many of my clients use an alternate profile for exercise with glucose targets that are less aggressive than their usual goals, often somewhere in the range of 120 to 200 mg/dl for types of exercise that lead to a drop in glucose. (Certain types of resistance training, such as hard low-repetition weight training of large muscle groups, can temporarily raise blood glucose.) It’s also important to be aware that, because the system is making adjustments automatically, less carbohydrate is typically needed to prevent/treat hypoglycemia during exercise.
Each person will have the best outcomes during exercise with their hybrid closed-loop system with a customized approach. Factors such as the time of day, duration of physical activity, and phase of the menstrual cycle (if applicable) will all need to be taken into account. With the help of their health care team, every user will need to do some trial and error and analysis to determine the approach that works best for them.
Time to get moving
There is more exciting technology in the works that will hopefully someday make glucose management during exercise a worry of the past. But until then, we should use the available tools to their fullest potential. Keep exercising, and definitely don’t let diabetes hold you back!
Want to learn more about exercising with diabetes? Read “Exercise for Beginners,” “Add Movement to Your Life,” “Picking the Right Activity to Meet Your Fitness Goals” and “Seven Ways to Have Fun Exercising.”
