Don’t Crash: How to Manage Exercise Lows


Editor’s note: This content was originally produced by JDRF, shared here as part of the JDRF – Beyond Type 1 Alliance. You can find more valuable content about exercising with T1D in JDRF’s exercise guide.

If you’ve participated in any physical activity while also living with type 1 diabetes, you know that managing blood sugar levels alongside exercise can be challenging.

While exercise can help manage overall blood glucose levels and make insulin work more efficiently in the body, low blood sugars during and after exercise can be disruptive and dangerous. Below, we’ll dive into the science behind the blood sugar drops so you can better understand and plan for them. 

With exercise, the impact on your blood glucose depends on how much energy is expended, the intensity and duration of the exercise and whether the movement is mostly aerobic, anaerobic, or both. Aerobic activity in particular is often associated with lowering blood sugar levels, but did you know that aerobic activity can actually lead to two distinct blood sugar drops, one during and one after exercise? Any activity that is at least slightly challenging and uses muscles in a continuous fashion can be considered aerobic—like raking leaves, walking, running and cycling. 

First, let’s understand the science of how the body controls blood sugar levels. Two hormones are most important—insulin and glucagon. Insulin reduces blood sugar levels, while glucagon raises them. 

Insulin reduces the amount of glucose in the blood by binding to receptors on the body’s cells, like how a key enters a lock to unlock a door. When activated, the insulin receptors bring glucose transporters to the cell’s surface, allowing glucose to be transported into the cell. This lowers the amount of glucose in the bloodstream and allows glucose to enter the cells, either to be stored or burned for fuel. 

Glucagon does the opposite; it raises the blood glucose level by getting the liver to break down its stored sugar called glycogen, and then dumps it into the bloodstream. 

What happens during exercise

Exercise makes our muscles burn glucose for fuel, and also makes insulin work more efficiently by increasing the number and responsiveness of the glucose transporters. Insulin also blocks the production of glucagon. This is what causes blood glucose levels to drop during exercise. 

Some types of exercise can also increase your blood sugar. Anaerobic exercise—like sprinting and lifting weights—creates lactic acid which your body converts into glucose to cycle back to your muscles to use for fuel.

What happens after exercise

The second delayed drop in blood glucose levels is due to two things—the body replenishing glucose stores that were used during exercise and increased insulin sensitivity, which can last for several hours after exercise. This can cause blood glucose levels to drift downward for up to 24 hours after a workout.

The best way to prevent low blood sugars

  • Even if you are doing low to moderate activity for a relatively short amount of time, you may need some extra carbohydrates or a reduction to your insulin dose before you exercise (the video below outlines specific ways to measure how many carbs you may need, or how much you may need to reduce insulin levels). 
  • Learn about exercising before you eat, when there’s less mealtime insulin still in your system.
  • Remember, if you experience a severe low blood sugar for any reason, your chances of experiencing another low within 24 hours are increased. It’s best to avoid exercise for a day after experiencing a severe low. 
  • You might notice different glucose responses when you do the same exercise at different times of the day. It may be worth experimenting to figure out how your blood glucose levels are affected differently depending on when you work out. 

No matter what, always be prepared with a rapid acting carbohydrate, such as glucose tablets, gels, or a sweetened drink in case you need to raise a low blood sugar. 

Watch the video below to learn a few specific calculations to help reduce low blood sugars during and after exercise!