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Diabetes Knowledge

How to Stop Diabetes From Ruining Your Workouts

6/15/2021 by mySugr

How to Stop Diabetes From Ruining Your Workouts

How diabetes affects exercise, and vice versa, is a big topic in itself. Sometimes, managing blood sugar levels around exercise and activity turns out to be more challenging than the workout itself.

On one hand, keeping your blood sugars in check while you’re on the move is tricky because your body reacts completely differently depending on the time of day and how fit you are. On the other hand, it’s hard because your blood sugar level varies depending on what kind of exercise or activity you’re doing.

Yikes! Talk about introducing a ton of variables into the mix. But exercise is so good for you that it’s worth the trouble. It’s a surprisingly powerful tool in your diabetes toolbox. People with diabetes can often find themselves spending a lot of time before, during, or even after exercise worrying about how to stay in range and avoid nasty lows. But despite all that, your blood sugar usually just does what it wants anyway. Naturally, this can be super frustrating!

Sometimes, situations can sneak up on us too! It’s so easy to forget that everyday activities like gardening, pushing a stroller or cart, or even doing your shopping also count as physical activity. It’s not only physical activity that burns a lot of sugar. Your brain needs a lot of energy too, so deep thinking can also lower your blood sugar levels.

What Exactly Does Exercise Do to Your Body?

Power sports (anaerobic)

In anaerobic sports (for example strength sports, lifting weights, climbing, but also stop-and-go sports such as volleyball, tennis and sprinting), blood sugars may remain stable or even increase, and then fall again afterwards while you’re recovering.

Anaerobic exercises are usually brief, intense bursts of physical activity when oxygen demand surpasses the oxygen supply. The body cells can’t use their usual methods of gathering the energy required to perform whatever the action may be (lifting weights, sprinting, etc.).

If the muscles need a lot of energy very fast, the body uses another way of delivering that energy. In situations like these, adrenaline rushes in to help, which causes sugar stores in the muscles to dump their load. You can already guess what happens next; your blood sugar rises quickly. This is especially common in competitive situations. Some athletes with diabetes even take a little bit of fast-acting insulin to stay on track.

Endurance sports (aerobic)

When it comes to  aerobic exercise (for example, jogging, walking, swimming, cycling), blood sugar usually drops both during the activity and for a long time afterwards. You can often do aerobic exercises for extended periods of time (10 minutes or more). These types of exercises are typically rhythmic and repetitive, and will increase your heart rate and pace of breath. Here, your body is burning oxygen along with glucose stores or fat to supply the energy needed.

For exercise newbies and those getting back into shape, low-intensity, steady workouts are ideal since your body will use fats as the primary energy source and burn sugar reserves at a slower pace. This allows you to exercise with more stamina and also reduces the risk of hypers.

With increased intensity and duration, more glucose is used, and your risk of low blood sugars also increases. The more often you exercise, the more efficient your muscles will become in terms of using energy. They will also get better at using fats for energy. Additionally, the glycogen stores in your muscles (200-400 g) grow bigger the more they are used.

At the beginning of any new physical activity, you’ll have to pay extra attention to planning and precautions until your body gets used to it.

What Happens to My Values After Exercising?

After exercising, while you’re recovering and basking in the glow of doing something great for yourself, your body is just getting started. Especially after any endurance exercise, your glucose stores will be empty and hungrily snatching up any sugar floating through your bloodstream for the next 7-11 hours. It may feel like your insulin is supercharged. In this case, you’ll need to be mindful of lows.

For extreme sporting events, like a marathon or a sports tournament, it may take several days until things are back to normal. This is partly due to small insulin-independent transporters that help shovel sugar into the cells to replenish the sugar stores in your muscles and liver.

Did you catch that? Those special transporters work even without insulin! That’s part of what makes exercise so cool!

What Else Is There to Consider?

If you start to experience symptoms of hypoglycemia, immediately stop your activity!

If you have type 1 diabetes and start exercising with high blood sugar levels, i.e. above 250 mg/dL (14 mmol/L), be sure to check for ketones. If you have ketones, it’s best to sit this one out. Exercising may accelerate/encourage more ketones, potentially leading to diabetic ketoacidosis, and that’s something you want to avoid for sure.


Diabetes and Exercise Tips and Tricks

  • It can be hard to recognize lows during exercise because the symptoms are hard to detect. Check your blood sugar often and be mindful about it until you get your routine figured out – especially if it’s a new exercise.
  • Keep fast-acting glucose nearby and readily available to treat low blood sugars. For more extended duration activities, you may need to consume carbohydrates during your exercise to prevent lows. Consider choosing only fast acting carbs, such as juice and glucose tabs, right before starting or during your exercise.
  • Rapid drops in blood sugar during exercise often result from too much active insulin on board. Be extra mindful of this if you’re starting a workout with lots of insulin on board, and prepare accordingly if you know you’ll be working out soon after taking any insulin. For pre-breakfast exercise, it can be helpful to reduce the average basal rate the evening before, depending on insulin type, exercise intensity, and current fitness level.
  • For endurance sports lasting more than 1-2 hours, you may need less insulin than usual for the meal before exercise. 
  • Full-time (all day) activities often require lowering meal and basal insulin for the next 24 hours after the exercise. Your diabetes team will help you figure out the right amount. 
  • For type 1 diabetes, eating at least 90 minutes after your workout may reduce the risk of overnight lows. Especially in the afternoons or evenings, consider reducing either your insulin intake (please discuss with your doctor the right amount) or eat small extra fat and protein snacks before you go to sleep without insulin. Be careful when correcting high values, you might need less insulin than usual. Everyone, however, is unique and you’ll need to experiment a little bit to find the right balance for you. 
  • After the strength training, which can initially lead to higher blood sugars, insulin requirements may fall over the following 6 hours as the liver replenishes its reserves. So be careful with your insulin intake.

Take special care with alcohol after exercise – this will prevent your liver from releasing sugar. In this case, increased insulin sensitivity and reduced sugar release overlap. Watch out for low blood sugars, keep your wits about you and your glucose tabs at the ready!



Thurm,U., Gehr, B., Diabetes-Sportfibel, 4. Auflage (all suggestions for therapy adjustment are taken from this source)

This article was updated in November 2021.

The mySugr website does not provide medical or legal advice. mySugr blog articles are not scientific articles, but intended for informational purposes only.
Medical or nutritional information on the mySugr website is not intended to replace professional medical advice, diagnosis or treatment. Always consult a physician or health care provider with any questions you may have regarding a medical condition.


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