Physical activity and exercise are essential for anyone with diabetes, but should you exercise when your blood sugar is high? Although there's ongoing research that physical activity can help lower blood sugar levels, the relationship isn't always as clear-cut as that, especially with regard to ongoing diabetes care. The connection between exercise and blood glucose levels can vary from person to person, activity type, intensity, duration, and more, which is why it's important to work with your doctor and better understand how one affects the other. Here, we'll go over some information on how exercise impacts blood glucose control and whether or not you should work out with high blood glucose.
Quick Overview: Should You Exercise When Your Blood Sugar Is High?
- Exercise often lowers blood sugar by helping your muscles absorb glucose and improving insulin sensitivity.
- Mild or moderately high blood sugar may not require skipping exercise if you feel well, are hydrated, and have no ketones.
- If your blood sugar is above 240 mg/dL, check for ketones before exercising and avoid activity if ketones are present.
- Aerobic exercise typically lowers glucose, while high-intensity exercise and strength training may temporarily raise it.
- Monitor your glucose before, during, and after activity, and stop exercising if levels rise rapidly or you develop concerning symptoms.
How Does Exercise Affect Blood Sugar?
When you exercise, your muscles need glucose for energy. To meet this demand, they absorb more glucose from your bloodstream, which means blood glucose tends to decrease. Depending on the type and intensity of your workout, this can continue hours after exercise, as your muscles continue to use sugar for recovery and repair. When you exercise regularly, this can have compounding effects that may lead to improvements in insulin sensitivity, helping your body use insulin more effectively even when you’re not working out.
However, there are certain activities that can result in a rise in blood glucose, such as high-intensity aerobic exercise, sprinting, and heavy strength training. The intensity of these exercises can trigger a stress response in the body that then signals the liver to release additional glucose. Although everyone has a different fitness level or exercise tolerance, it's important to understand why some workouts may raise blood glucose and what to do if it occurs.
Aerobic Exercise
Aerobic exercise includes activities that repeatedly engage large muscle groups, making your heart and lungs work harder. This typically includes things like walking, jogging, running, swimming, dancing, or cycling. In general, aerobic exercise tends to lower blood glucose levels, but longer or more intense workouts can temporarily cause elevated numbers.
Although generally safe, people who take insulin or diabetes medications may be at risk of low blood sugar during exercise, or several hours after. Therefore, it's important to be diligent about checking your blood sugar and keep an eye out for any signs of hypoglycemia. And, as always, never start a new program without first talking to your doctor.
Strength Training and High-Intensity Exercise
Strength training and high-intensity activities can affect blood sugar differently. Heavy weightlifting, sprinting, and high-intensity interval training place greater short-term stress on the body, triggering hormones such as adrenaline and cortisol. These hormones signal the liver to release more glucose, which may cause blood sugar to temporarily rise during or shortly after exercise.
Although these exercises increase glucose, it doesn't necessarily mean they're harmful. Resistance exercise can build muscle mass, which in turn helps insulin sensitivity and long-term blood glucose trends. Still, it's important to work with your doctor and try to keep blood glucose levels within your target range for a majority of the day.
What Are Ketones and Why Do They Matter?
Ketones are substances your body produces when it breaks down fat for energy. Small amounts can be normal, but when your body doesn't have enough insulin, ketones can build up to dangerous levels.
High ketone levels may lead to diabetic ketoacidosis (DKA), a serious, potentially life-threatening complication of diabetes. DKA occurs when ketones accumulate and make the blood too acidic.
Warning signs of DKA can include nausea, vomiting, stomach pain, excessive thirst, frequent urination, fruity-smelling breath, rapid or deep breathing, and confusion.
Exercising when ketones are elevated can make the situation worse. If you have high blood sugar and elevated ketones, avoid exercise and follow your diabetes care team's instructions. Seek emergency medical attention if you experience symptoms of DKA.
How Do You Check for Ketones?
You can check ketone levels at home using either a blood ketone meter or urine ketone test strips.
- Blood ketone testing: A blood ketone meter measures ketones using a small drop of blood from your fingertip, similar to checking blood sugar. You'll need a meter and compatible ketone test strips.
- Urine ketone testing: Urine ketone strips change color when exposed to urine. Compare the strip to the color chart on the package at the specified time to determine the approximate ketone level.
Blood ketone testing generally provides a more current measurement, while urine testing reflects ketones produced earlier.
A standard blood glucose meter or continuous glucose monitor (CGM) does not measure ketones unless the device specifically supports ketone testing.
Ask your diabetes care team whether you should keep ketone testing supplies at home, when to test, and what actions to take based on your results. If your ketones are elevated, avoid exercising and follow your prescribed sick-day or high-glucose management plan.
Is It Safe to Exercise When Your Blood Sugar Is High?
In short: it depends. Having elevated blood sugar doesn't always mean you need to skip exercise. However, whether physical activity is safe depends on your glucose level, diabetes type, ketone levels, symptoms, and individual treatment plan.
If your blood sugar is significantly elevated, follow your healthcare provider's instructions for checking ketones before exercising. Avoid exercise when ketones are elevated or if you have symptoms that could indicate diabetic ketoacidosis (DKA).
People with type 1 diabetes and those who use insulin pumps may need additional precautions. Certain diabetes medications can also increase the risk of ketoacidosis, sometimes even when blood sugar is not unusually high.
Talk with your diabetes care team about the glucose and ketone levels at which you should postpone exercise, as well as when to seek medical attention.
When Light or Moderate Exercise May Be Appropriate
Part of your diabetes self-management plan should always include checking your blood glucose prior to exercise. It’s also important to test your blood sugar after exercise, and during if you're planning a longer session. A continuous glucose monitor can help provide ongoing readings, but always talk to your doctor if you have questions or concerns. In general, It's okay to exercise when:
- Your blood sugar is elevated but below 240 mg/dL
- Your blood sugar is above 240 mg/dL, but you have checked for blood ketones, none are present, and your healthcare provider has approved exercise
- You feel well and are adequately hydrated
- Your glucose is stable rather than rising rapidly
- The activity is consistent with your established diabetes management plan
- Your healthcare provider has approved a low- or moderate-intensity activity, such as walking
Continue monitoring your blood sugar and stop exercising if it rises rapidly, drops below 70 mg/dL, or you begin to feel unwell.
When You Should Avoid Exercise
Regular exercise is great and can help reduce the risk of diabetes complications, but there are some instances when it should be avoided. Postpone your workout and follow your diabetes care plan when:
- Your blood sugar is above 240 mg/dL, and ketones are present
- Your glucose remains above 250 mg/dL for repeated readings or continues rising despite corrective measures
- Your blood sugar continues to rise despite corrective measures
- You have signs of diabetic ketoacidosis (DKA), such as nausea, dizziness, abdominal pain, fruity-smelling breath, confusion, or difficulty breathing
- You are ill, vomiting, dehydrated, or unable to keep fluids down
- Your healthcare provider has advised you to avoid physical activity
- Your blood sugar is extremely high, and you do not know why
Any ranges provided are general guidelines, so it's important to work with your doctor to understand your specific ranges. Exercise should never be used as an emergency treatment for severe hyperglycemia. When blood sugar is extremely high, or ketones are present, physical activity may cause glucose to rise further and increase the risk of DKA.
What to Do If Your Blood Sugar Is High Before a Workout
If you notice a high reading during blood glucose checks prior to engaging in diabetes exercise, take the following steps.
- Confirm the glucose reading, especially if it doesn't match how you feel
- Check the CGM trend arrow or repeat a finger-stick test when appropriate
- Test for ketones if glucose is above the threshold recommended by your provider
- Consider possible causes, including meals, missed medication, stress, illness, dehydration, or an infusion-set problem
- Follow your prescribed correction plan rather than improvising an insulin dose
- Drink water and avoid starting exercise while dehydrated
- Choose gentle activity only if you feel well, have no ketones, and your care plan allows it
- Recheck blood sugar before increasing the intensity
Again, these are general guidelines and recommendations, but the process you use in your diabetes treatment plan should be pre-discussed with your doctor to avoid any issues or complications.
Does Diabetes Type Affect Exercise Safety?
Yes, diabetes type can affect how your body responds to exercise and which precautions you may need to take. Physical activity benefits most people with diabetes, but factors such as insulin use, diabetes medications, ketone production, and existing health complications can influence exercise safety. Some safety considerations include:
- People with type 1 diabetes: Monitor blood sugar, insulin on board, and CGM trends before exercising, and avoid exercise if you have ketones present.
- People with type 2 diabetes: Watch for low blood sugar if you use insulin or certain medications, and modify activities if you have diabetes-related complications.
- People with prediabetes: Most people can exercise safely, and regular aerobic and strength training may improve insulin sensitivity and help prevent type 2 diabetes.
What Are the Best Exercises for Lowering Blood Sugar?
There are several benefits of exercise, and creating a routine that works with your lifestyle can provide stronger long-term blood sugar management for people with diabetes. However, high-intensity exercise can cause blood sugar to rise for a short period of time. If you're looking for more stable exercises for diabetes care that can lower your blood sugar, try one or more of the following:
- Walking
- Jogging
- Cycling
- Swimming
- Yoga
- Mobility classes
Although some of the more gentle types of exercise may not have as strong a response to glucose as other aerobic activities, they're generally considered safe and can still provide the positive effects of exercise when done regularly. At the end of the day, the important thing is finding something that you enjoy and that you can sustain, as the biggest benefits from physical activity come from consistency. It's also important to talk with your doctor before starting anything new.
When to Stop Exercising and Seek Medical Attention
Diabetes and exercise tend to go hand-in-hand, but there are a few instances where it may be necessary to stop what you’re doing and see your doctoreeex. Stop exercising and contact your healthcare provider if you experience:
- Blood sugar that continues to rise or remains very high despite following your treatment plan
- Moderate or high ketone levels
- Severe weakness, dizziness, confusion, or difficulty coordinating your movements
- Persistent nausea, vomiting, or abdominal pain
- Rapid or difficult breathing
- Fruity-smelling breath
- Signs of severe dehydration, such as extreme thirst, dry mouth, or inability to keep fluids down
- Chest pain, fainting, or severe shortness of breath
Call 911 for chest pain, loss of consciousness, severe breathing difficulties, or other signs of a medical emergency.
Maintain an Active Lifestyle With the Right Diabetes Support
Exercise can support better blood sugar management for people with diabetes or prediabetes, but monitoring your glucose and following your healthcare provider’s recommendations are essential. Byram Healthcare offers high-quality diabetes products to help you stay informed, prepared, and confident while remaining active. Contact us today to learn more.
