How to Exercise With Type 1 Diabetes

Cardio, weight training, and more

Exercise is an important component of a healthy lifestyle for adults and children with type 1 diabetes, according to the American Diabetes Association (ADA). Even so, physical exertion directly affects blood glucose (sugar) and so people who have diabetes—and especially those who have complications of diabetes such as neuropathy—will need to take special precautions. If you have type 1 diabetes, this means choosing activities that are safe for you and making adjustments to your supplemental insulin, medication, and food intake to match the type of exercise you do and the time and intensity of your workouts.

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Benefits

Each of the three main types of exercise—aerobic, strengthening, and activities that focus on flexibility and balance—are known to have benefits for people with type 1 diabetes above and beyond those for otherwise healthy individuals, as detailed in the 2016 ADA's position paper on physical activity and diabetes.

Aerobic Exercise
Resistance Training
Flexibility and Balance
In addition to the general health benefits, for people with type 1 diabetes cardiovascular exercise has been shown to:

- Increase cardiorespiratory fitness
- Decrease insulin resistance
- Improve endothelial function
- Reduce risk of death
People with diabetes often have low muscle strength and tend to lose strength more quickly, and so regular resistance training can help to remedy that. It isn't clear how weight training and similar strengthening activities affect blood sugar level control. As people with type 1 diabetes get older their joints tend to lose mobility more quickly than those of other people. Those who have neuropathy also may be more prone to falls. Activities that address flexibility and balance can help prevent both loss of mobility and falls.

The ADA recommends people with type 1 diabetes get a total of 150 minutes of exercise per week, incorporating all three types of activities.

Safety

During physical activity, the body draws on glucose for energy, resulting in a dip in blood sugar levels. If you have diabetes, you know this could be dangerous but with careful planning overseen by your doctor, you can avoid an extreme decrease in glucose (hypoglycemia).

Specifically, your dose of supplemental insulin and any other medication you take likely will need to be modified. You also will need to plan meals and snacks according to your exercise schedule or vice-versa.

Note that if you have certain complications of diabetes, you may need to limit physical activity or avoid it altogether. These include:

  • Inadequate control of blood sugar levels
  • An unstable heart condition
  • High blood pressure
  • Retinopathy
  • Peripheral neuropathy (nerve damage to extremities, foot ulcers, etc.)
  • Autonomic neuropathy (nerve damage to internal organs)
  • Microalbuminuria and nephropathy (poor kidney function)

If you have peripheral neuropathy, it's important to examine your feet regularly for injuries associated with physical activity that you may not notice otherwise.

Planning

How your body responds to exercise will be unique to your physiology. For that reason, it's important to check your blood sugar before and after exercise as well as monitor it frequently while you work out—ideally every half hour when you first begin a new routine. This will allow you to respond if your glucose begins to go too low in the moment. It also will help you identify patterns in how your blood sugar fluctuates during activity.

Managing your glucose in regards to exercise may involve ingesting supplemental carbohydrates, changing your insulin dose, both, or neither. Accordingly, the ADA says:

  • If you plan work out for less than 30 minutes you may not need to adjust your carbs or insulin.
  • The same holds true if you do high-intensity exercise lasting less than 10 minutes, such as intervals, weight training, or HIIT (although you may experience an increase in blood sugar.)
  • For activity lasting longer than 30 minutes, especially if it's aerobic, you likely will need to lower your insulin dose, ingest supplemental carbs, or both.

Variable intensity activities such as basketball, field sports, or tennis are less likely to destabilize blood glucose than are those that involve steady exertion.


Note that although convenient, the ADA says continuous glucose monitors may not be reliable for monitoring blood glucose during exercise, as they can have issues (sensors breaking, being unable to calibrate, delayed or inaccurate glucose-level reporting).

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:

  • If your circulating insulin is low before you do low- to moderate-intensity exercise lasting between 30 minutes and 60 minutes, eat 10 grams to 15 grams of carbs beforehand to keep blood sugar levels steady.
  • If you’ve recently taken insulin, you may need 30 grams to 60 grams of carbs for each hour you exercise in order to maintain performance and blood sugar.

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

  • If you use injected insulin, reduce your dose before and after your work by 20%.
  • If you use a continuous insulin pump, lower or stop your dose when you start exercising or, alternatively, stop your dose 30 to 60 minutes before you begin your workout.
  • 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% to 75% to prevent dangerous dips in blood sugar.

Stop Working Out When

If you feel weak, shaky, or dizzy, or your blood sugar level drops below 90 mg/dL while you're working out, stop and eat 15 grams of fast-acting carbs.

You should be able to exercise safely if your blood glucose is between 90 mg/dL and 250 mg/dL, but depending on the exact level as well as the type of activity you do and how long you plan to work out, it may be advisable to eat some carbohydrates before you start and to monitor your blood sugar during your exercise session, according to guidelines from the ADA and with your doctor's guidance as well.

Starting Glucose Levels and Exercise
Below 90 mg/dL If you plan to exercise for more than 30 minutes, have 15 grams to 30 grams of carbs before you start. Eat more carbs as needed based on your testing results. For shorter and very high-intensity sessions, you may not need more.
90–150 mg/dL Have carbs when you start exercising, taking into account how long you plan to exercise, and your current insulin level. Eat carbs as needed for longer sessions.
150–250 mg/dL Start exercising without carbs. If during your workout your blood sugar drops to below 150 mg/dL, then you can supplement with carbs.
250–350 mg/dL Test for ketones: If they're moderate to high, do not exercise. However, if they're low, you should be able to exercise at a mild to moderate intensity until your blood sugar drops to below 250 mg/dL, at which point you should be able to increase the intensity.
More than 350 mg/dL Test your ketones; do not exercise if they’re at moderate to high levels. If they’re negative or at trace levels, consider taking insulin at 50% of your usual dose. Stick to low-to-moderate intensity activity until your blood sugar reaches 250 mg/dL.

Preventing Low Blood Sugar Post-Exercise

A dangerous drop in blood sugar can occur within six to 15 hours after exercise, or even up to 48 hours post-workout, in people with type 1 diabetes.

Low blood sugar overnight is particularly important to watch for. If you take insulin via injection, the ADA suggests reducing basal insulin by 20% on exercise days, 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% for six hours after exercising.

Either way, have a snack before bed; you may even want to wake up during the night to check your blood sugar or set your continuous monitor alarm to awaken you if your blood sugar drops too l

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.

A Word From Verywell

If you have type 1 diabetes you've likely been living with it your entire life. This means you already have a handle on how your body responds to activity, which will surely help you to start a new exercise routine or safely make changes to your existing regimen. Even so, whether you're starting from scratch or you're an exercise veteran, it's important to consult your doctor first and to keep them apprised of your progress and any issues you encounter. This way you can glean all the benefits of living an active lifestyle without compromising your health.

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