Exercise and insulin pumps: what the guidance says

A pump makes it possible to change insulin delivery quickly, which is useful for activity, but it does not make the glucose response predictable. A Cambridge University Hospitals leaflet for pump users says that unpredictable levels are frustrating but entirely normal, and that no perfect strategy works every time. Settings, percentages and targets belong to the person and their diabetes team, so they appear here only as clearly labelled examples from published guidance.

Why activity changes glucose

Diabetes UK says that activity at a comfortable pace, such as walking, jogging, yoga, cycling or swimming, tends to lower blood glucose. Short, sharp efforts such as sprinting, squash or high intensity interval training tend to raise it, and stretching may leave it unchanged. Stress, for example in a tournament, can push glucose up too. The Cambridge leaflet explains that muscles use glucose for energy in low to moderate exercise, whereas high intensity exercise triggers a surge of hormones such as adrenaline.

A figure in the 2022 ISPAD exercise guideline for children and adolescents, reproduced on its PubMed record, makes the same point in summary: aerobic exercise is generally associated with a drop in glucose, while anaerobic and mixed forms can be associated with less of a drop or even a rise. It adds that individual responses depend on duration and intensity, starting glucose, fitness, time of day, insulin levels and nutritional status. Diabetes UK adds that the same activity can give different results on different days. Terms such as blood glucose are defined in the glossary.

Temporary basal rates and other adjustments

A pump delivers small amounts of background insulin all the time, set in blocks of time called basal rates. Diabetes UK notes that these rates can be changed depending on how active a person is, and lists easier tailoring of insulin before, during and after exercise as an advantage of pumps. A temporary basal rate raises or lowers the background rate for a set period and then returns to the usual pattern. The basics are in how an insulin pump works.

The Cambridge leaflet shows why no single number exists. It publishes tables, credited to a 2017 review, in which the suggested reduction to mealtime and background insulin varies with the type of activity, its intensity and its length. As one example from that guidance, not advice, it suggests that after afternoon or evening exercise a temporary basal reduction of 20% for six hours at bedtime could be used to lower the overnight risk of lows.

Insulin already working in the body matters too. The same leaflet advises avoiding exercise when active insulin from a recent bolus is at its peak, which it says is usually one to two hours after the dose.

Suspending, disconnecting and closed-loop settings

The Cambridge tables include, for some types of activity, a 100% basal reduction at the start of exercise, which amounts to a suspend of background delivery. Diabetes UK says that a pump wearer should have the pump attached most of the time and only take it off for small breaks, such as swimming or showering. For people on a hybrid closed loop system, Diabetes UK says to consider using the activity or temporary target setting for around 90 minutes before and during exercise. See closed loop for the term.

Checking glucose and carrying fast-acting carbohydrate

Diabetes UK's general guidelines, which it says are only a guide and differ for pump users, suggest that blood glucose before exercise should ideally be around 5.6 to 12 mmol/L, and that exercise should not begin at 4 mmol/L or lower, or at 3.5 mmol/L or lower for anyone using an insulin pump. Below 4 mmol/L it describes treating the low first with a usual hypo treatment, followed by starchy carbohydrate and a recheck after 15 minutes. Above 13 mmol/L it advises talking to the healthcare team and, if the high is unexplained and the person has been taught how, testing for ketones.

The advice for carrying supplies is consistent across sources: keep hypo treatments and a carbohydrate snack to hand, wear diabetes identification, and keep a record of what happens during activity to show the team. The Cambridge leaflet suggests monitoring before, during (every 30 minutes) and after exercise. Its advice to avoid exercise entirely for 24 hours after a severe low is echoed by Diabetes UK. A hypo can occur during or after activity.

Delayed lows after exercise

Lows do not always arrive during the activity. The Cambridge leaflet explains that the body restocks the glucose stores in the muscles and liver afterwards, which can lower glucose soon after exercise or several hours later, and that long endurance efforts may keep levels low for a day or so. Diabetes UK says glucose should be checked after exercise and, for up to 24 hours afterwards, because the body can respond better to insulin for that long. The leaflet adds that exercise in the afternoon or evening can carry a higher risk of lows overnight, and Diabetes UK notes that a continuous glucose monitor lets the wearer see the effect of any activity.

Protecting the set, contact sports and water

The set or patch pump has to stay in place through movement. Diabetes UK notes that infusion sets can become unattached, which can lead to high glucose, so how a set will cope with a knock or a pull is a fair question for the team. The sources opened for this page do not give sport-specific rules for contact sports, so how and where to protect the site is something to ask the team about. Choosing and changing sites is covered in infusion sets and site rotation.

For swimming and bathing, Diabetes UK says the user manual shows whether a pump is water resistant or waterproof; one that is not should be disconnected first, and a tubed pump is best disconnected. Many patch pumps are waterproof, but depth and time limits differ by model.

In short

Gentle activity tends to lower glucose, short bursts tend to raise it, and the effect on the day can last into the night. A pump allows temporary basal changes, suspending or disconnecting for short periods, and closed-loop activity settings, but the published percentages are examples rather than rules. Checking before, during and after, carrying fast-acting carbohydrate, and asking the diabetes team for a personal plan are the points the sources agree on.