Tips: Endurance Exercise with a Closed-Loop Pump
Training for a marathon or a triathlon as a person with type 1 diabetes comes with a variety of challenges and learning curves. As if training your body to run, bike, hike, or swim for hours and hours isn’t hard enough!
Today’s closed-loop insulin pump options may simplify many aspects of endurance training with type 1 diabetes, but there’s still plenty to learn along the way. A few small studies have found using a closed-loop pump during endurance sports to be safe, but it still requires self-study and a variety of careful adjustments.
Here, we’ll discuss in-depth details on using a closed-loop insulin pump while training and competing in endurance sports. (Read more about exercising with diabetes here!)
You still need to evaluate, experiment, and adjust with a closed-loop pump.
The biggest thing in exercising with type 1 diabetes is that while the science of exercise doesn’t change, every person will have different approaches that work well for their body,” explains Jennifer C. Smith, RD, CDCES.
Smith has helped hundreds of people with type 1 diabetes train for marathons and triathlons through her work at Integrated Diabetes Services. She’s also lived with type 1 diabetes (T1D) for over 30 years and has competed in both marathons and triathlons in recent years.
“Regardless of how you take your insulin, every suggestion—including with a closed-loop pump—needs to be evaluated,” adds Smith.
“You have to do some careful self-experimentation to find what works for you. When you learn how your closed-loop pump’s algorithm is thinking, how it will make adjustments, then you have to learn how to adjust what you do and what you tell the system to do for you. It’s another layer of management.”
Different closed-loop pumps require different adjustments.
“The technology development of insulin pumps have come a long way,” says Smith. “You have to learn how the algorithm of your closed-loop system is thinking in terms of how and when it will adjust your doses.”
Things to consider when exercising with type 1 diabetes, especially with endurance sports:
- Type of activity you’re doing (aerobic vs. anaerobic)
- Intensity level
- Length of time
- Starting blood sugar level
- Direction of starting blood sugar level (rising vs. falling)
- Active insulin onboard / Timing of your last meal
Smith further explains the different algorithms of today’s closed-loop systems and what adjustments are ideal for endurance training vs. average exercise.
For all closed-loop systems: decreased meal boluses taken two to three hours before exercise
“A suggestion that applies to all closed-loop systems is to decrease the size of a bolus given for any meals eaten two to three hours before any type of aerobic exercise,” explains Smith.
“This helps by reducing the lingering effects of larger boluses, because rapid-acting insulin in your pump is still active in your system for about four hours.”
Smith says this includes the timing of when you eat versus when you exercise, too.
“While these systems will adjust for changes in your blood sugar, they don’t know you are planning to go out for an 8-mile run after lunch, so you need to plan accordingly.”
She recommends reducing the meal bolus and selecting one of the following settings when you eat that meal:
- “Exercise” Mode in the Tandem t:Slim X2 Control-IQ
- “Temp Target” within “Auto” Mode in the Medtronic 670G/770G
- “Overrides” in DIY closed-loop systems
Using the Tandem t:slim X2 Control-IQ during endurance training
The “Exercise/Activity” Mode:
- This mode is best for mild-to-moderate activity, like walking, gardening, mowing the lawn, on the playground, or shopping, to prevent low blood sugars during and after.
- You can also combine this mode with a reduced basal rate profile for long days of mild-to-moderate activity like a day at the beach, a day of skiing, etc.
- This mode needs to be turned on at least 60 minutes prior to the start of your exercise or activity.
- This mode works by suspending insulin doses when your blood sugar begins to drop below 100 mg/dL. It sets your blood sugar target for 150 mg/dL, and it avoids pumping extra corrective insulin if your blood sugar rises towards or past 150 mg/dL before or during exercise.
The “Normal” Mode:
- This mode is very effective for managing your blood sugars during workouts that might normally increase your blood sugar — like anaerobic workouts (sprinting, lifting weights, etc.) or during fasted exercise in the morning.
- Normal mode is targeting a blood sugar of 112 mg/dL, so it will dose corrective insulin if you begin rising past this target range.
- This mode is not suggested for intense aerobic (cardio) workouts—like spinning, jogging, endurance exercise, etc. It is too aggressive in its effort to maintain the target range of 112 mg/dL, and you are more likely to experience a severe drop in your blood sugar.
- This mode can also lead to low blood sugars during endurance training when you’re also consuming frequent servings of carbohydrates for fuel.
Turn Control-IQ OFF during aerobic & endurance exercise:
- As explained above, Control-IQ is too aggressive for high-intensity aerobic exercise and endurance training. It will most likely lead to low blood sugars.
- Suggestion: turn on “Manual Mode” and then set a “temp basal” decreased rate to last for 75 percent of your planned exercise time.
- How much you set this “temp basal” rate for will vary greatly from person-to-person depending on your overall conditioning, the length of your exercise session and how much fuel (carbohydrates) you plan to consume during that time-frame.
- Determining your “temp basal” rate will require careful experimentation. For some, the ideal “temp basal” rate may be 10 percent, and others it may be as high as 50 percent. For example, this means you’re decreasing your normal basal rates by 20 percent or by 50 percent. The higher the percentage, the less insulin you’ll be getting.
Using the Medtronic 670G or 770G during endurance training
The “Auto” Mode:
- This mode automatically targets a blood sugar of 120 mg/dL. This is too low for most types of exercise and will likely lead to low blood sugars.
- This mode is very effective for managing your blood sugars during workouts that might normally increase your blood sugar—like anaerobic workouts (sprinting, lifting weights, etc.) or during fasted exercise in the morning.
- This mode is not suggested for intense aerobic (cardio) workouts—like spinning, jogging, endurance exercise, etc. It is too aggressive in its effort to maintain the target range of 120 mg/dL, and you are more likely to experience a severe drop in your blood sugar.
- This mode can also lead to low blood sugars during endurance training when you’re also consuming frequent servings of carbohydrates for fuel.
Use “Temp Target” within “Auto” Mode:
- Suggestion: While in “Auto” Mode, you can select “Temp Target” and adjust the target blood sugar from 120 mg/dL up to 150 mg/dL to decrease the amount of insulin it will dose which counters your increased insulin sensitivity you’ll likely experience during aerobic (cardio) activity.
- Just like the Control-IQ, you’ll want to start this mode at least 60 minutes before you begin exercising.
- Additional carbohydrates can also help prevent lows in this system. You’ll want to pay close attention to how much “active” insulin to determine if you’ll need additional carbohydrates before you begin exercising.
- When consuming carbohydrates to off-set “active” insulin already onboard, it is wise to consume a bit less than you think you might need. Consuming too much could trigger the system to dose additional insulin, causing eventual low blood sugars.
Using the DIY closed-loop systems during endurance training
Many of the recommendations for the FDA-approved systems can be applied effectively to these do-it-yourself closed-loop systems, including:
- You should anticipate needing to adjust your DIY closed-loop settings about 60 minutes prior to exercising in order to prevent low blood sugars.
- “Overrides” are a feature in DIY systems that allow you to tell it to give you less insulin in anticipation of exercise.
- “Overrides” can also allow you to adjust your target blood sugar to a higher number (from 90 mg/dL to 150 mg/dL, for example) to decrease the amount of insulin you have on board before and during exercise.
Post-Exercise Recommendations with a Closed-Loop Pump
“It’s also important to manage your post-exercise insulin, because it can impact your insulin sensitivity for anywhere from 12 to 24 hours after intense or endurance workouts,” says Smith.
“Using the ‘exercise’ mode or ‘temp target’ for the hours after your workout can help you avoid low blood sugars as your body works to replenish your glycogen stores from your post-workout meals.”
“In general,” adds Smith, “the most important thing when doing any type of exercise as a person with type 1 diabetes is to plan ahead as much as possible.”
