A Guide to Exercise and Type 1 Diabetes

Taking a break mid-run

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Exercise can and should be a big part of a long-term treatment plan for type 1 diabetes. In fact, there are numerous athletes living with type 1 diabetes who've reached the top of their game while having the disease. Physical activity can help increase insulin sensitivity and control blood sugar, but it's key to be mindful of how exercise works to reduce blood glucose and what you can do to prevent low blood sugar levels during, and especially after, exercise.

Benefits of Exercise

According to the recently released exercise guidelines for type 1 diabetes in The Lancet, every adult with diabetes (including those with type 1) should be exercising for 150 minutes per week, with no more than two consecutive days of no activity.

Exercise has numerous benefits for everyone, but especially for people with type 1 diabetes, including:

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

Exercise may also raise or lower your glucose levels. When you have type 1 diabetes, it's important to regularly monitor your glucose to stay within your safety zone.

Glucose Levels During Exercise

When you exercise, your body uses the glucose (sugar) stored in your liver, muscles, and blood. The sugar stored in your liver and muscles is called glycogen. Throughout an exercise session, you'll use up your body's stored glucose, and as a result, your blood glucose levels start to drop.

  • During the first 15 minutes of activity, most of the sugar 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 your muscles and liver start to get depleted and your body will switch over to using stored fat for fuel; this is called fat-burning.

According to the exercise guidelines in The Lancet, people with the disease who exercise may become hypoglycemic within 45 minutes of starting the activity. However, those who are already aerobically conditioned have less glucose variation during exercise.

What's also key to realize is that it can take four to six hours—for some, up to 24 hours—to replace the used sugar in the form of glycogen in the muscles and liver. During this period, your blood sugar may continue to drop from that same exercise session. Research has shown that insulin sensitivity may also be increased for 24 to 48 hours post-exercise. Speak with your doctor to determine a plan of action to address this factor.

Types of Exercise

There are three main types of exercise. Each has its own benefits, and each has its own effects on your body. Different types of activity may affect each person differently, so be sure to regularly test your blood glucose levels with a glucometer before, during, and after each form of exercise. Work with a personal trainer and your healthcare team to create an exercise regimen that works for you.

Cardio

Aerobic or cardiovascular exercise is any activity that raises your heart rate and breathing level for more than 10 minutes. This type of activity may reduce your glucose and glycogen stores quickly, so it's important to use a continuous glucose monitor or another method of regular tracking. Examples of cardio activity include:

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

High-intensity cardio exercises such as sprinting or HIIT (high-intensity interval training), which involves periods of intense exercise and short rests, may actually raise glucose if the body's 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

Anaerobic exercises such as weight-based activities may still reduce or raise glucose, depending on the intensity of the activity. Examples include:

  • Free weights
  • Weight machines
  • Elastic resistance bands
  • Bodyweight exercises

Weight lifting may cause an increase in blood glucose for several hours after exercise. This may require an insulin correction. However, it's essential that any insulin corrections be especially prudent, as an over-correction may result in something called severe nocturnal hypoglycemia, where glucose plummets during sleep, which could be life-threatening.

Flexibility

Another form of anaerobic exercise, flexibility-based programs improve muscle tone and strength without significantly raising heart rate or breathing rate. Examples include:

  • Some forms of yoga
  • Stretching

Flexibility exercises may also result in glucose-raising and should incorporate frequent monitoring.

Before You Begin

Before starting any new exercise regime, review these helpful tips.

  • Talk to your doctor. If you don't currently have a regular exercise routine in place, connect with your doctor before starting. Your care provider can help you set target glucose ranges and heart rate levels to meet your personal health needs.
  • Check your blood sugar before you exercise. You want your blood glucose reading to be above 100 mg/gL and below 250 mg/dL. This helps to ensure that you are starting your exercise with a blood glucose level that is less likely to send you into a hypoglycemic episode. If your blood sugar is below 100 mg/dL you'll want to eat a piece of fresh fruit, a slice of wheat toast with peanut butter, or another snack with at least 15g carbohydrates, wait 15 minutes, and check your blood again to ensure that it is above 100 mg/dL before exercising.
  • Try not to exercise at the peak of your insulin action. Peak action is the time when insulin works hardest to remove glucose from your bloodstream—you're more likely to have low blood sugar during this time. Exercising when your insulin peaks will increase your risk of a rapid drop in your blood sugar. Try to anticipate when you will exercise and plan it around the peak action points. Determine your peak action time with your doctor.
  • For longer workouts, eat an extra snack before you exercise. If you anticipate an exercise session of more than 30 minutes, you might consider consuming an extra 15g carbohydrates (examples include 4 to 6 crackers with cheese slices, a single-serving cup of low-fat yogurt, or nut butter on graham crackers) to help cover for the additional glucose you will be using. Regardless, you will want to pause your activity after 30 minutes and check your blood to ensure that your blood sugar is in an acceptable range.

How to Prevent Low Blood Sugar After Exercise

  • Avoid afternoon or evening exercise. You should attempt to stop exercising at least four hours before you intend to sleep at night so that you can assess how your exercise is affecting 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, you might consider doubling your snack or, if possible, reducing your insulin dosage to lessen the risk of a low blood sugar reaction while you sleep.
  • Take a pass on a post-workout sauna, steam room, or hot-tub session. Each of these treatments is relaxing, but they all continue to 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. It makes sense to most people with type 1 diabetes that they should check their blood sugar shortly after exercise to ensure that it is at a safe level. But far fewer would think to check their blood sugar again two to four hours after exercise to check for a delayed drop of their blood sugar. If you notice that your blood sugar is lower at this two- to four-hour post-exercise check, you should check it again 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 are effective at hydrating the body and replenishing glucose stores to prevent delayed hypoglycemia.

Target Ranges

Be sure to monitor your glucose before, during, and after all exercise, even if you've performed the same exercise before. Thanks to numerous variables such as time of day, duration of activity, the food you've recently consumed, how much sleep or rest you've logged recently, your blood sugar numbers may fluctuate. Wearing a continuous glucose monitor may be helpful.

While glycemic target ranges will vary person to person, here are the target ranges to aim for before starting exercise are 126 mg/dl to 180 mg/dl. Here's what to do if you're not at that level:

  • If your starting blood glucose target is below target range at 90 mg/dl or less: Ingest 10-20g 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 124 mg/dl: Consume 10g of carbs (i.e. a protein bar with 10g carbohydrates) and aerobic high-intensity or anaerobic exercise may be started.
  • If your starting blood glucose target is at the target range of 126 to 180 mg/dl: Aerobic, high-intensity, or anaerobic exercise may be begun, but monitor glucose to watch for an increase.
  • If your starting blood glucose target is slightly above the target range at 182-270 mg/dl: Aerobic or anaerobic exercise may be begun, but monitor glucose during anaerobic exercise to watch for an increase.
  • If your starting blood glucose target is above the target range at 270 mg/dl: This is technically hyperglycemia, which may be explained by a recent meal. If you haven't eaten recently, check your blood ketones through a urine test. If only slightly elevated (up to 1.4 mmol/L), a brief-duration light intensity exercise may be started. Do not start exercise if blood ketones are above 1.5 mmol/L—work with your healthcare team to immediately manage your elevated glucose levels.

    What to Do If Glucose Drops Too Low

    If you've been monitoring your glucose during exercise and your numbers are starting to plummet, stop exercising immediately and eat a snack with at least 15g of fast-acting carbohydrates, such as half a banana, a 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.

    Remember the "Rule of 15" when treating hypoglycemia to avoid over-treatment: Eat 15g 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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