A Guide to Exercise and Type 1 Diabetes

Taking a break mid-run

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Regular exercise is a vital aspect of type 1 diabetes management. It can help improve insulin sensitivity, control blood glucose (blood sugar), and provide other benefits specific to ongoing diabetes care as well as to overall health.

At the same time, physical activity can pose certain challenges to someone with type 1 diabetes: Without careful planning around meals and snacks, it can lead to dangerous dips in blood sugar (hypoglycemia) both during a workout and afterwards.

According to guidelines published in The Lancet in 2017, both adults with type 1 diabetes and those with type 2 diabetes should log 150 minutes of exercise per week, with no more than two consecutive days of no activity.

Benefits

The many health payoffs of regular exercise are as applicable to people with type 1 diabetes as they are to everyone else, namely:

  • Improved insulin sensitivity
  • Better weight management
  • Stronger muscles and bones
  • Reduced blood pressure
  • Heart health and reduced cholesterol
  • More energy

Glucose Levels During Exercise

In order to fuel physical activity, the body calls on the glucose in the blood as well as that stored in the liver and muscles—called glycogen. During extended physical activity, those stores of glucose and glycogen will be called upon as fuel and will eventually begin to decrease in a predictable manner:

  • During the first 15 minutes of activity, most of the glucose used for fuel comes from the blood or the muscles.
  • After 15 minutes, the sugar stored in the liver is tapped for fuel.
  • After 30 minutes, the glycogen reserves in the muscles and liver begin to be depleted. At this point the body turns to fat stores for energy.

According to The Lancet exercise guidelines, people with diabetes who exercise may become hypoglycemic within 45 minutes of starting activity, although aerobic conditioning can help to mitigate glucose variation during exercise.

The effect of exercise on blood sugar levels continue to be significant well after workouts: It can take four to six hours—and for some people, up to 24 hours—for the body to replenish glycogen in the muscles and liver, during which time blood glucose levels may continue to drop. Research has shown that insulin sensitivity may also be increased for 24 to 48 hours post-exercise.

Types of Exercise

There are three types of exercise, each having different effects and benefits for the individuals who participate in them. Test your blood glucose levels with a glucometer before, during, and after each form of exercise so you'll know for sure how activity impacts you.

Aerobic (cardiovascular) exercise

Cardio is defined as any activity that raises your heart rate and breathing rate for more than 10 minutes. Examples include:

  • Brisk walking
  • Jogging or running
  • Biking
  • Swimming
  • Tennis
  • Basketball

Aerobic exercise tends to draw on glucose and glycogen stores quickly, so it's important to use a continuous glucose monitor or other method of regular tracking during aerobic workouts.

One exception: High-intensity cardio exercise such as sprinting or HIIT (high-intensity interval training), which involves periods of intense exercise and short rests, may actually raise glucose if the levels of the stress hormone cortisol increases during the activity, as cortisol causes more glucose to be released into the bloodstream. People with type 1 diabetes may need to counteract this effect with an increase in insulin.

Strength Training

Although defined as anaerobic exercise, activities designed to build strength and increase lean muscle mass may reduce or raise glucose, depending on the intensity of the activity. Examples include:

  • Lifting free weights
  • Training on weight machines
  • Using elastic resistance bands
  • Doing exercises that call on body weight for resistance

Weight lifting may cause an increase in blood glucose for several hours after a session that may require an insulin correction. However, it's essential that any insulin corrections be prudent, as an over-correction may result in severe nocturnal hypoglycemia, a potentially life-threatening condition in which glucose plummets during sleep.

Flexibility Training

Another form of anaerobic exercise, flexibility-based exercise focuses on stretching muscles and connective tissue in order to improve and maintain mobility. Many such activities, such as certain forms of yoga, also improve muscle tone and strength without significantly raising heart rate or breathing rate.

Although most flexibility activities are relatively low-key, they can still bring on a bump in glucose levels. They also may increase glucose levels and should incorporate frequent monitoring.

Before You Begin

Whether you're new to exercise or newly diagnosed with diabetes and in need of guidance for how to incorporate your current regimen into you new lifestyle, there are commonsense steps you can take to prevent injury and get the most out of physical activity.

  • Talk to your caregivers: Connect with your diabetes team before you begin exercise. They can help you set target glucose ranges and heart rate levels to meet your personal needs.
  • Check your blood sugar before you exercise: This helps to prevent a hypoglycemic episode in which activity depletes your energy stores. Ideal blood glucose readings prior to exercise are between 90 mg/gL and 250 mg/dL. If yours is below 90 mg/dL, eat a snack containing at least 15 grams of carbohydrates (a piece of fruit, say, or wheat toast with peanut butter). Wait 15 minutes and check your blood again to make sure it's over 90 mg/dL before exercising.
  • Try not to exercise at the peak of your insulin action: Peak action is the time during which insulin works hardest to remove glucose from the bloodstream and so levels are likely to be low. Exercising when your insulin peaks will increase your risk of a rapid drop in your blood sugar. Try to anticipate when you have peak action points and plan workouts accordingly.
  • For extended periods of activity, eat an extra snack before you get moving: If you plan to work out for more than a half hour, down an extra 15 grams of carbs even if your blood glucose level is in the optimum range for exercise. Even if you do this, take a break after 30 minutes and check your blood to ensure it's in an acceptable range.

How to Prevent Low Blood Sugar After Exercise

What you do after you work out is just as important for your safety, well-being, and efficient recovery as what you do before.

  • Don't exercise in the afternoon or evening: Plan to complete workouts at least four hours before you intend to go to sleep. This way you can assess how activity affects your blood sugar. If you exercise right before bedtime, you increase the risk of a nighttime hypoglycemic reaction that could be serious. If your blood sugar is less than 100 mg/dL before bed, consider doubling your snack or, if possible, reducing your insulin dosage to lessen the risk of a low blood sugar reaction while you sleep.
  • Skip the post-workout sauna, steam room, or hot-tub session: As relaxing as these treatments are, all will keep your heart rate elevated and may contribute to lower blood glucose as a result.
  • Check your blood glucose immediately after you exercise and for several hours afterward: Check your blood sugar shortly after exercise to ensure that it is at a safe level, and again two to four hours later. If it's still low at the two- to four-hour post-exercise check, re-check it in another two to four hours or until you are certain your glycogen from exercise has been replaced and you no longer see a lowering of your glucose.
  • Hydrate and fuel up post-exercise: Milk-based drinks with carbohydrates and protein—such as chocolate milk—are particularly effective at hydrating the body and replenishing glucose stores to prevent delayed hypoglycemia.

Target Ranges

Monitor your glucose before, during, and after all exercise, even if you do the exact same workout day after day. Numerous variables—such as time of day, duration of activity, the food you've recently consumed, and how much sleep or rest you've logged recently—can cause fluctuations in your blood sugar levels. Wearing a continuous glucose monitor is helpful.

While glycemic target ranges will vary from person to person, the target range to start exercise without eating prior is between 150 mg/dl and 250 mg/dl. If you're not at that level:

  • If your starting blood glucose is below target range at less than 90 mg/dl: Ingest 15 to 30 grams of carbs (i.e. an apple with peanut butter) before starting to exercise and wait until glucose levels exceed 90 mg/dl.
  • If your starting blood glucose is slightly below target range at 90 to 150 mg/dl: Consume 10 grams of carbs (i.e. a protein bar with 10 grams of carbohydrates) and aerobic high-intensity or anaerobic exercise may be started.
  • If your starting blood glucose target is at the target range of 150 to 250 mg/dl: Aerobic, high-intensity, or anaerobic exercise may be begun, but monitor glucose throughout your activity to watch for an increase.
  • If your starting blood glucose target is above the target range at greater than 250 mg/dl: This is technically hyperglycemia, which may be explained by a recent meal. If you haven't eaten recently, use your ketone levels with a urine test. If they're only slightly elevated (up to 1.4 mmol/L), it should be find to do a brief low-intensity exercise session.

Do not exercise if your blood ketones are above 1.5 mmol/L. Contact your healthcare team to immediately to manage your elevated glucose levels.

What to Do If Glucose Drops Too Low

If during exercise your blood glucose begins to plummet, stop immediately and eat a snack with at least 15 grams of fast-acting carbohydrates, such as half a banana, 1 tablespoon of honey, 2 tablespoons of raisins, or 4 to 6 ounces of fruit juice. Carry glucose tablets or a glucagon injection kit with you and wear a medical ID bracelet stating that you have type 1 diabetes in case of any hypoglycemic emergency.

Follow the "Rule of 15" when treating hypoglycemia to avoid over-treatment: Eat 15 grams of carbs, wait 15 minutes, then check blood sugar again, and repeat until your blood sugar has returned to normal levels. Then, eat a small protein-rich snack, such as a hardboiled egg or peanut butter toast, to stabilize levels until your next meal.

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