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How to Best Manage and Prevent Exercise Low Blood Sugars

Mar 31, 2011

If you take insulin or another blood glucose-lowering medication, you are at risk for low blood sugar (usually defined as blood glucose < 65 mg/dl), or hypoglycemia, which can occur during or following physical activity. Low blood sugar can cause trembling, sweating, dizziness, blurred vision, impaired thinking, and even seizures and loss of consciousness.

Exercise presents its own special challenges for managing blood sugar. Since any activity increases your body’s use of blood sugar, hypoglycemia can develop more easily. The more you understand about what makes your blood sugars go down (or sometimes up) during exercise, the easier it becomes to control and the more confident you can be about doing activities and staying in control of your diabetes.


Much of your blood sugar response has to do with how much insulin is in your bloodstream. If your insulin levels are high during a physical activity, your muscles will take up more blood glucose (since muscle contractions themselves stimulate glucose uptake without insulin) and you’re more likely to end up with low blood sugars. You can even end up with late-onset hypoglycemia, which can occur from right after to up to 48 hours after you exercise. What’s important is to do your best to prevent lows before, during and after exercise by taking the steps listed below.

Prevent Lows Before, During and After Exercise

  • Learn how your body responds to exercise by checking your blood sugar levels before, (occasionally) during, and after exercise.
  • If your blood sugar is near or below 70 mg/dl before you exercise, bring it back within normal range before you begin by consuming some carbohydrates.
  • Always be prepared to correct a low by carrying a rapid-acting carbohydrate with you during exercise. Don’t assume you’ll be able to find pure glucose, soda, juice or candy nearby if you need it.
  • If you exercise long and hard, your body will use a lot of carbohydrate, so you’ll likely need to eat some carbs both before and during the activity to prevent both early fatigue and hypoglycemia.
  • Whenever exercising for an hour or more, check your blood sugar every 30 minutes or so to catch and treat lows early.
  • If you begin to feel your blood sugar dropping and are able, sprint as hard as you can for 10 to 30 seconds. Your body will release glucose-raising hormones. (You may also need to take in some glucose as well.)
  • Pick a good time of day to exercise. You are less likely to develop hypoglycemia when you exercise moderately early in the morning before breakfast because that is when your body is naturally most insulin resistant.
  • If your blood sugar is lower for several hours after activity, you may need to take less medication (mostly rapid-acting insulin) than usual during that time.

Intense Workouts May Raise Your Blood Sugar

Exercise does not always just cause hypoglycemia. Immediately after intense exercise, you may experience high blood sugar for a few hours instead due to the fact that intense exercise causes your body to release glucose-raising hormones, such as adrenaline. Your body may need more insulin to bring your blood sugar levels back to normal. For instance, after cycling to near-exhaustion, a group of people with type 1 diabetes using insulin pumps experienced elevated blood glucose levels for two hours after the activity. Similarly, in a group of intense cyclers with type 2 diabetes, blood glucose levels rose for one hour afterward.

If you only take oral medications, try doing 10-15 minutes of more moderate exercise after an intense workout to help lower blood sugars naturally. Also, keep a close eye on your blood sugar for 24 to 48 hours after intense activity. After the initial high blood sugar, your blood sugar may drop as your body works to restore the glucose in your muscles that was depleted during your activity.

Optimize Your Diabetes Regimen for Physical Activity

  • Keep fast-acting carbohydrate with you at all times. Glucose tablets work well because they will not spoil, need no refrigeration, and won’t be damaged by hot and cold temperatures; some other hard candies also work, but at a slightly slower rate since sucrose (table sugar) is only half glucose, with the other half being fructose.
  • Eat some carbohydrates during exercise to prevent lows. Taking in carbs during exercise can keep your blood sugars from dropping. Pure glucose and other fast-acting carbs are digested quickly and usually start to hit your bloodstream within five minutes. The amount of carbohydrate that you need depends on how long and hard you’re exercising, what time of day it is, and how much insulin is in your system. Frequent monitoring of your blood sugar before and after exercise will help you know your needs.
  • If you take insulin, be familiar with its action. Insulins vary in terms of how fast they start to work, when they peak and how long their effects last in your body. It’s easier to avoid lows when exercising when your insulin is not peaking.
  • Oral diabetic medications with the longest duration (such as Diabinese, DiaBeta, Micronase, and Glynase) have the greatest potential to cause hypoglycemia. Talk with your healthcare professional if you use these and plan to become more physically active.
  • Increasing your activity level may require you to lower your medication. If you make a change in your exercise routine, consult with your healthcare professional about adjusting your insulin dose and/or oral medications. Even oral medications that do not usually cause exercise-related low blood sugars may need to be considered.
 Be aware of the possible symptoms of hypoglycemia, which may vary during exercise. Whenever exercising for an hour or more, check your blood sugar periodically. If you do not feel the symptoms of hypoglycemia (called hypoglycemia unawareness), talk with your healthcare professional about how often to check your blood sugar during and after exercise.

How to Correct a Low

If your blood sugar is < 65 mg/dl:

  • Stop exercising immediately and eat 15-20 grams of pure glucose or another food containing fast-acting carbohydrate. Pure glucose is the preferred carbohydrate to correct low blood sugar, or you can use other fast-acting carbs found in regular soda, 4-7 hard candies or a glass of low or fat free milk or juice.
  • Wait 15 minutes, and then check your blood sugar again. If your blood sugar is still below 100 mg/dl, or your goal-range, correct again with another 15-20 grams of fast-acting carbohydrate. Do not restart your exercise until your blood sugar is above 100 mg/dl or in your target range.

Sign up for the newly-launched DIABETES “Fit Brain, Fit Body!” fitness/lifestyle programs or for 5 free Healthy Living Reports at www.lifelongexercise.com, and access more articles and information at www.shericolberg.com. If you need tips for getting safely started on an exercise program, check out The 7 Step Diabetes Fitness Plan. For people with any type of diabetes who are already more active, consult the Diabetic Athlete’s Handbook.

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