How to Exercise With Type 1 Diabetes

Benefits and guidelines for cardio, weight training, and more

Exercise can be a helpful component of treatment for type 1 diabetes. This is in spite of the fact physical exertion tends to lower blood glucose (sugar) levels.In truth, according to the guidelines from the American Diabetes Association (ADA), most children, adolescents, and adults with type 1 diabetes should not be discouraged from physical activity, given how important regular exercise is for overall health and well-being.

However, in order to work out safely, people with type 1 diabetes will need to take certain precautions, including making adjustments to supplemental insulin, medication, and food intake to match exercise time and intensity.

Many world-class athletes have type 1 diabetes. In the United States, these include Olympian swimmer Gary Hall Jr, the National Football League’s Jay Cutler, and the skier Kris Freeman. The Australian rugby player Steve Renouf and cyclist Monique Hanley are others.

How to Stay Safe Exercising with Type 1 Diabetes

If you have type 1 diabetes, it's imperative you consult with your doctor and other members of your health care team before you start an exercise program. Assuming you're dependent on supplemental insulin, your dose of this and other medications you may be taking likely will need to be modified so you can exercise safely without causing dangerous dips in your glucose levels. You also will need to consider your food intake as well.

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Benefits of Exercise for Type 1 Diabetes

According to the ADA, regular exercise offers multiple benefits for adults and children living with type 1 diabetes:

  • Improves insulin sensitivity
  • Strengthens muscles
  • Boosts cardiovascular health and lowers the risk of heart disease
  • Lowered risk of exercise-induced low blood sugar (hypoglycemia) (with weight training)
  • Improved flexibility and joint mobility. Some clinical trials have shown yoga and similar gentle forms of exercise can improve insulin sensitivity, build muscle, and lower blood cholesterol levels. They’re also great for stress relief and improving quality of life.
  • Exercise benefits children and young adults with type 1 diabetes. One meta-analysis of children under 18 with type 1 diabetes found significant reductions in HbA1c among those who exercised. Engaging in physical activity more than three times a week for more than an hour and combining aerobic and resistance training yielded the most benefits

Diabetic complications may also require special consideration. The following is a partial list of complications that may limit exercise type, duration, or intensity:

  • Uncontrolled blood glucose (high or low)
  • Uncontrolled high blood pressure
  • Unstable heart conditions
  • Retinopathy
  • Peripheral neuropathy (nerve damage to extremities, foot ulcers, etc.)
  • Autonomic neuropathy (nerve damage to internal organs)
  • Microalbuminuria and nephropathy (poor kidney function)

For example, individuals with retinopathy or high blood pressure should not perform the Valsalva maneuver, in which an exercise is performed by forcibly exhaling against a closed airway and straining to lift a weight.

People with diabetic nerve damage should also learn how to care for their feet and look for foot ulcers or other injuries with physical activity.

Planning for Exercise with Type 1 Diabetes

How your blood sugar level responds to exercise will be unique to your physiology as well as depend on when you exercise and what sort of activity you do. This means you'll need to test your glucose regularly as you work out and adjust carbs and insulin accordingly.

Timing

However, in regards to timing, the ADA does advise:

  • Exercising before a meal (in other words, while fasting) is likely to produce a small increase or decrease in blood sugar
  • Exercising immediately after a meal that’s preceded by a standard insulin dose will lower blood sugar. However, long periods of exercise under these conditions can produce significant drops in glucose.

In addition to testing before and after an exercise session, also test your blood sugar every half-hour when you’re beginning a new exercise regimen. Over time, you’ll learn your body’s response to different types and varying duration of exercise.

Duration and Intensity

The ADA reports the following based on its review of current research:

  • Workouts lastly less than 30 minutes may not require a carb or insulin adjustment
  • Very high-intensity exercise lasting less than 10 minutes, such as intervals, weight training, or HIIT, may not require adjusting insulin or carbs. However, short-duration, high-intensity may also raise blood sugar.
  • Long-duration exercise—more than 30 minutes, and particularly when aerobic—will generally require reductions in insulin, carb supplementing, or both. Exercise that varies intensity, such as field sports, is more likely to result in better glucose stability than exercise that is solely aerobic.

Using a Continuous Glucose Monitor

The ADA notes that continuous glucose monitors can have issues: for example, sensors breaking, being unable to calibrate, or delayed or inaccurate glucose-level reporting. If you use a continuous monitor, speak with your health care providers about alternative options if needed.

Balancing Carbs, Insulin, and Exercise

Testing blood sugar levels frequently as you train will help you adjust carbs and insulin according to your body's needs. To help you get started, the ADA offers these preliminary guidelines:

  • When circulating insulin is low, ingesting 10 to 15 grams of carbs before exercising at low to moderate intensity for 30 to 60 minutes may maintain blood sugar levels.
  • If you’ve recently taken insulin, you may need 30 to 60 grams for each hour you exercise to maintain performance and blood sugar—which is what most athletes need, the ADA points out, regardless of whether they have type 1 diabetes.

You may also need to adjust your insulin dose before or following exercise to account for the blood sugar changes likely to result. The ADA suggests starting with the following adjustments, then fine-tuning according to your testing results.

  • If you use injected insulin, try reducing your before-exercise and after-exercise doses by 20 percent.
  • If you use a continuous insulin pump, you can reduce or stop your dose when you start exercising. Alternatively, try stopping your dose 30 to 60 minutes before starting to exercise.
  • If you exercise within two to three hours of taking insulin (whether by pump or injection), you may need to lower your usual basal dose by 25 percent to 75 percent to prevent hypoglycemia.

It’s important to emphasize that your specific needs may vary—that’s why it’s essential to test glucose levels before, during, and after exercise.

Stop exercising and ingest about 15 grams of fast-acting carbs if you feel weak, shaky, or dizzy, or when your blood sugar drops below 90 mg/dL.

Before exercising, your blood glucose should be between 90 mg/dL Aand 250 mg/dL. The ADA suggests the guidelines in the following table based on starting glucose levels.

Starting Glucose Levels and Exercise
Below 90 mg/dL If you plan to exercise for more than 30 minutes, have 15 to 30 grams of carbs before you start. Have more carbs as needed based on your testing results. For shorter and very high-intensity sessions, you may not need carbs.
90–150 mg/dL Have carbs when you start exercising, taking into account how long a session you’re planning and your existing insulin level. Continue with carbs as needed for longer sessions.
150–250 mg/dL Start exercising without carbs. When blood sugar drops to below 150 mg/dL, then supplement with carbs.
250–350 mg/dL Test for ketones, and don’t exercise if they’re moderate to high. If they’re low, exercising at mild to moderate intensity is fine, but don’t perform high-intensity exercise until blood sugar drops below 250 mg/dL, since high-intensity exercise may raise blood sugar. 
More than 350 mg/dL Test your ketones, and don’t exercise if they’re at moderate to high levels. If they’re negative or at trace levels, considering taking insulin at 50 percent of your usual dose. As with lower glucose levels, avoid high-intensity exercise until blood sugar reaches 250 mg/dL.

Preventing Low Blood Sugar Post-Exercise

A key benefit of exerise for most people is it lowers blood sugar. However, for people with type 1 diabetes there is a risk physical activity can cause glucose levels to drop too low. This can occur within six to 15 hours of exercise but can occur as long as 48 hours after an exercise session.

Low blood sugar overnight is particularly important to watch for. If you use injections, the ADA suggests reducing your basal insulin dose by 20 percent on the days you exercise, eating a low-glycemic meal in the evening after you’ve exercised, and reducing your post-meal bolus insulin. If you use a continuous monitor, reduce your basal insulin rate by 20 percent for six hours after exercising.

For both groups, having a snack before going to sleep can help. You may also want to check your blood sugar levels at some point during the night or set your continuous monitor to alarm you if blood sugar drops too low.

You can also work these tips into your exercise routine. Each has been shown to reduce the risk of exercise-induced delayed low blood sugar:

  • Begin or end a moderate-intensity session with 10 seconds of all-out effort, such as a sprint.
  • Incorporate short, high-intensity periods intermittently into an otherwise moderate exercise session.
  • Perform resistance exercise (weight training) before aerobic forms of exercise.

Weight Training and Workouts

Exercise falls into three primary types: aerobic, resistance (weight training), and flexibility. Ideally, you’ll do all three within a given week.

Aerobic exercise includes walking, jogging, running, and swimming—anything that gets your heart rate up to a higher level than what you’re accustomed to. Resistance and weight training can be as simple as a yoga session (your Plank and Down Dogs count!), or a session with weights at a gym.

Remember to start where you are, adjusting your expectations and activity for existing fitness, age, and goals.

If jogging is too much, for example, start with walking, then gradually increase your pace and distance over time. If walking is too much, start by increasing your daily activity—try a short walk around the block after a meal, or do chair yoga. Even gardening, cleaning, or playing with your kids are forms of activity that can improve blood sugar and glycemic control—start there if more feels like too much.

As your activity levels increase, you may be surprised to see how quickly you progress to feeling better and having more energy. That’s when to extend exercise duration or increase intensity. The ADA recommends 150 minutes of exercise per week that includes all three. When you reach this point, you’re receiving excellent health benefits from your effort. A weekly program could look like the plan set out in the following table. Adjust to your individual needs.

A sample weekly aerobic and weight training plan
Day 1 Aerobic training: 30–45 minutes
Day 2 Weight training: 45–60 minutes
Day 3 Aerobic training: 30–45 minutes
Day 4 Aerobic training: 30–45 minutes
Day 5 Weight training: 45–60 minutes
Day 6 Aerobic training: 30–45 minutes
Day 7 Rest
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