Exercise + Diabetes: How to Avoid Low Blood Sugar

Exercise can be challenging if you live with diabetes and take insulin or use other blood-sugar-lowering medications. Nothing makes exercising more frustrating than crashing and having to stop your workout because of low blood sugar. Then you have to gobble up some fast-acting carbs just to survive, which can feel like you’re ruining your workout.

If you’re looking for ways to avoid the low blood sugar cycle before, during or after exercise, this guide provides some actionable tips to ease the stress of lows and help you maximize your workouts with diabetes.

What causes low blood sugar before and during exercise?

Exercise makes your body burn glucose faster, which can increase the risk of low blood sugar.  When you exercise, your muscles pull in more glucose for energy. Combined with other factors like too much or too little insulin in your system and not having enough carbs for fuel, your body’s stored energy in the liver can’t release enough sugar to keep up.

If you experience low blood sugar during exercise, it could be from:

• Medication type and dose
• Insulin on board (IOB)
• Your “starting blood sugar” before working out 
• Your carb intake before and during exercise
• Recent low blood sugar not related to physical activity. This is because your body’s alert response may be weaker, making another low more possible. 
• Your fitness level. The more fit you are, the more often you use more glucose during exercise. (Who knew?)

Understanding the reasons behind why your lows are happening during activity is the first step to understanding what you can do about them. The goal is to continue with the activities you enjoy.

Blood glucose levels and exercise: your step‑by‑step action plan 

The lower your blood glucose is at the start of your workout, the more likely a low is to occur during exercise. The American Diabetes Association recommends these steps depending on your starting blood glucose level before exercise:

What you should do if you eat before exercise

Whether you want or need to eat before exercising, you usually need to take less insulin for that meal. Exercise increases the body’s sensitivity to insulin, a typical amount of insulin is likely to cause low blood sugar when you work out. If your workout falls within 90 minutes after taking insulin for a meal, make sure to reduce your pre-workout meal bolus. 

How much you reduce your insulin will depend on how long you plan to exercise, what kind (like weight lifting or jogging) and how your insulin doses match your body’s needs. If your insulin doses aren’t right, things might not go as planned. Talk to your healthcare team to help adjust your doses. Small changes can make a big difference for your safety and success.

Be patient with the process of figuring it out—you’ll get there.

Here’s how the American Diabetes Association recommends reducing your pre-exercise bolus insulin dose: 

What if your blood sugar is low before you want to exercise?

The real answer? It really depends on why you’re low.

 If you’re low for any of the following reasons and want to exercise, here’s what you should do:

• If you have an active bolus in your body: It’s probably best to treat the low and wait until that insulin is out of your system before you exercise if you’re low because you still have a bolus of insulin active in your bloodstream from a recent meal. 
• If you’re barely low: You may be able to still do your fasted exercise after eating five to ten grams of fast-acting carbohydrates if you’re only slightly low–we’re talking in the 70 to 75 mg/dL range (3.9 to 4.2 mmol/l) for most PWD. That is, if you’re up to it and feel safe. Sure, it’s not true fasted exercise because you’ve eaten, but if you keep carb intake low so it doesn’t require a bolus, you can still exercise with minimal risk of another low blood sugar episode.
• For example: If you wake up feeling a little low, you can let the dawn phenomenon help raise your blood sugar—if you experience it—and then do your usual morning exercise. You might still need a small amount of fast-acting insulin to prevent your hormones from pushing your blood sugar above your target range. If you wake up with a blood sugar below 3.1 mmol/L (55 mg/dL), treat it with a few jelly beans or glucose gummies. Whatever you prefer for your low blood sugar treatment! Wait until your blood sugar goes above 4.4 mmol/L (80 mg/dL), then do your workout.

High blood sugar levels before exercise

It’s important to correct high blood sugar, but be cautious before exercising. You can take less insulin to bring your blood sugar into a safe range without causing it to drop too low. This allows you to enjoy the benefits of exercising on an empty stomach.

• Remember: If your blood sugar is over 13.9 mmol/L (250 mg/dL), you may be at risk of developing ketones. Exercising with extremely high blood sugars can be dangerous for this reason. It may feel like a good time to exercise, but that’s not the case. If you’re hovering around this blood sugar level or higher, it’s probably best to postpone your workout until your blood sugar is closer to your goal range. You don’t want to mess around with ketones!
• For example: If you wake up with a blood sugar level of 11.1 mmol/L (200 mg/dL), you might give yourself a quarter unit of fast-acting insulin. This can help prevent it from going higher during your workout and help it return to a healthy range without dropping too low. It may take some trial and error to determine the best pre-exercise correction doses for you, but it’s worth the effort! Everyone needs movement. Our bodies crave it.

Exercising with diabetes is about trial and error

Learning how to manage your blood sugar during exercise is a learning process. It requires patience and a curious mind, looking for solutions rather than getting mad and giving up. 

It can be done! The more consistency you can create in your routine around the time of day you prefer to exercise, the easier it will be to study what works and what doesn’t. And above all else: always, always, always keep fast-acting carbohydrates (or emergency glucagon) with you in case you do go low.

Everyday moments add up! Join our virtual fitness challenge today and help raise money for people living with diabetes.