How Does Exercise Affect Type 1 Diabetes?

Michael C. Riddell, PhD;  Mark Harmel, MPH, CDCES


July 06, 2022

This transcript has been edited for clarity.

We've known for almost 100 years now that exercise is beneficial for people living with type 1 diabetes. It improves whole-body insulin sensitivity. It can reduce glucose levels, improve blood pressure, and help with weight management. Sometimes exercise can make glucose control much more difficult. It often causes low blood sugar, and from time to time, some forms of exercise may even cause high blood sugar.

We've recently completed the largest study to date on the effects of exercise in type 1 diabetes, looking specifically at three different but common forms of exercise that people tend to do for health and fitness reasons. These included aerobic exercise, such as walking, jogging, and cycling; resistance exercise like weight training; and high-intensity interval training, which is a bit of a mix of the two forms of exercise, a workout that you might do for health and fitness reasons with some high-intensity effort, and then some moderate effort intermixed in between these high bursts.

We found that there are huge patterns of variation in the glycemic responses to exercise in people living with type 1 diabetes. We already kind of knew that, but now, with this large dataset, we can explain why this variance occurs. We now know that factors such as sex, exercise time of day, exercise mode or type, how much insulin on board during exercise start time, and the pre-exercise glucose concentration all help to predict the rate of change in glucose during the different forms of exercise that we studied in this large cohort study.

One of the most surprising things we found is that in this study, aerobic exercise caused the greatest drop in glycemia, which we expected, but resistance exercise also was associated with a small drop in glucose. Other studies done in laboratory settings have suggested that resistance exercise may cause glucose to rise. Sure, we had some individuals who had a rise in glucose, but now we know that it's probably the time of day, the intensity of effort, and some other variables that can predict whether the glucose will drop, rise, or stay flat during these different forms of exercise.

Overall, we think that the more we can understand and measure for an individual on the timing of exercise, the duration of exercise, and some of the other factors that we know can predict their change in glucose, we may be better able to inform new exercise guidelines to keep glucose under better control, and maybe more importantly, design automated insulin delivery systems that are more customized to the patient, their unique characteristics, and the exercise that they tend to do, whether it's resistance, aerobic, or high-intensity interval training.

This exercise study, the Type 1 Diabetes Exercise Initiative, is the first real-world study to try to come up with an explanation for the variabilities around glucose control with exercise, with the overarching goal of improving time in range and minimizing both hypo- and hyperglycemia associated with the different forms of exercise that we want people with type 1 diabetes to do.

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