Which Type of Exercise Is Best for Managing Diabetes?
Whether you’re a pro or just getting started, here’s what you need to know about exercise and diabetes.
Exercising is one of the best ways to manage your diabetes. But which type of exercise – aerobic (like walking, running, swimming, and cycling) or anaerobic (like weightlifting and strength training) – is most effective at managing your blood glucose?
Regardless of what kind of exercise you do, the most important thing is to do some form of it consistently. It also helps if you have fun doing it.
When you exercise regularly, you may find that managing your blood glucose is easier, and you may also reduce the risks of long-term complications like heart disease, nerve damage, and other serious conditions.
Exercising when living with diabetes can feel like a challenge, but it can quickly become an easy habit with a little bit of planning. Famous athletes who have diabetes include five-time Olympic gold medalist Gary Wayne Hall Jr., Super Bowl champion Noah Gray, former NBA player Gary Forbes, and the Women’s National Basketball Association’s 2022 third overall pick Lauren Cox.
How does exercise affect blood glucose?
Exercise is beneficial for people with diabetes because it can lower glucose levels not only during, but up to 24 hours after a workout. Over time as you exercise more, insulin sensitivity increases and your body becomes better at balancing glucose. Factors that can influence your blood sugar response to exercise include the type of activity, time of day, whether you’ve recently taken insulin, what food was recently consumed, stress, and sleep.
A key difference between aerobic and anaerobic exercise is the fuel source that your body is using to power your workout. Aerobic activity primarily uses fat and blood glucose to provide energy for exercise. Prolonged aerobic activity can also use glycogen (a stored form of glucose in the muscles and liver that gets released to raise blood glucose, usually in response to stress or intense activity). This is why aerobic activity can cause glucose levels to fall (when blood sugar is used as fuel) and other times lead to hyperglycemia (when glycogen is released and used as fuel).
On the other hand, short-duration and anaerobic exercises (like quick sprints or weightlifting) may raise your blood glucose because they trigger the release of stress hormones, such as adrenaline, that release glucose from glycogen stores in your liver.
Cooling down can reduce your risk of hyperglycemia after vigorous exercise. You should cool down for about 20 minutes, which can include walking at a low effort pace and stretching. If your glucose levels remain high, you can consider conservative insulin correction (greater than 220 mg/dL).
However, your own results may vary based on how much muscle you have, nutrition, your current level of fitness, and the duration and intensity of physical activity.
What is aerobic exercise?
Aerobic exercises include any activity that gets your heart rate beating faster. A few examples include:
- Walking at a medium to fast pace on level ground, at a slower pace on steep hills, or in a pool for added resistance
- Jogging or running
- Water aerobics or swimming
- Biking or cycling on an indoor bike (try gradually increasing the incline over time for added resistance)
- Dancing
- Sports such as tennis, soccer, and basketball
- Outdoor activities like hiking and ice skating
As a general guide, the ADA recommends doing 30 minutes of aerobic exercise most days of the week. If you haven’t been exercising regularly, start with a short exercise session and add a few minutes each day until you can continually exercise for 30 minutes. Once you hit 30 minutes, slowly start to increase your time, or stay at 30 minutes and increase the intensity level of the exercise. For maximum benefit, do both.
You can make small changes in your daily habits that can give you big benefits, like taking the stairs instead of the elevator whenever possible, walking or biking to the grocery store instead of driving, and taking two-minute breaks every 30-60 minutes to do squats, jumping jacks, or walking the stairs to get your heart rate up. These small bursts of activity are called “exercise snacks,” and every bit counts!
If you have a gym at home or at work, try to exercise before work, before your lunch break or before you go home. Two or three 10-minute exercise sessions may be just as beneficial as one longer session, and they may be easier to fit into your schedule.
What is anaerobic exercise?
Anaerobic exercise is a short but intense type of training that can improve your strength and endurance. This movement can include strength training that uses your own body weight, resistance bands, or added weight to create resistance during exercise. These exercises can include:
- Weight lifting
- Sprints
- High intensity interval training (HIIT)
- Squats
- Planks
- Push-ups
- Pull-ups and chin-ups
- Jumping rope
You can combine anaerobic training with aerobic activity for added benefit. For example, you can walk with a weighted vest, hold dumbbell weights while you do squats, or do an exercise where you walk carrying weights (known as farmer’s walks). Group classes (like yoga, Pilates, Zumba, and barre) can be helpful, since there is an instructor who can guide you through movements if you do not know where to get started.
Burning fat and adding more muscle is a great way to better manage your blood glucose because muscles use more glucose than fat, even when you are not exercising. Some things to consider before you start a strength training regimen:
- Always consult with your healthcare provider before you start a new fitness program.
- A beginner needs to train two or three times per week to gain the maximum benefits.
- Rest each muscle group for at least 24-48 hours to maximize gains in muscle strength and size.
- Varying your workouts can help you push past a training plateau.
Your initial goal should be about 20-30 minutes of strength training, two to three days a week. If you’re not familiar with weightlifting, seek out a trainer to show you how to exercise properly or sign up for a group fitness class. This can help you avoid injury and maximize your benefits.
It is normal to feel fatigued or sore when you work out a muscle group that you haven’t exercised recently, but pain (especially sharp pain) is not normal. If an exercise is painful, stop and consult a healthcare provider.
What time of day is best for exercise?
There is some evidence that afternoon training can help reduce fasting blood glucose levels, but exercise studies tend to vary a lot in their experimental design, so it can be hard to make strong conclusions about when is best to train. What is clear is that any exercise is better than no movement.
Hormones produced in the morning (such as cortisol) help raise glucose levels. Practically, this can mean glucose levels decrease less with morning aerobic exercise compared to an afternoon workout. In the afternoon, levels of cortisol fall, so you may need to temporarily reduce your insulin dose or eat a snack before aerobic exercise to prevent hypoglycemia.
Keep in mind that high-intensity anaerobic morning exercise can cause hyperglycemia to the point of needing an insulin correction dose. In contrast, an afternoon anaerobic training can increase overnight time in range, but has an increased risk for evening hypoglycemia.
It’s difficult to say whether there is an ideal time to exercise – a morning workout might be great for one person, while an evening workout might be more beneficial for someone else. The best time of day to exercise is when you are most likely to consistently work out.
How to address hypoglycemia during exercise
Hypoglycemia is defined as glucose levels below 70 mg/dL. However, symptoms of hypoglycemia may not occur until glucose levels fall below 54 mg/dL. This could happen if you exercise so intensely that your heart rate remains elevated for a long time.
Especially if you have type 1 diabetes or use insulin to manage type 2 diabetes, always check your glucose before and after you exercise to prevent hypoglycemia. If you give insulin through manual injections, consider how long it has been since you gave your insulin dose, or if you use an insulin pump or automated insulin delivery (AID) system, check how much insulin you have on board before starting exercise.
Be prepared in case your blood glucose starts to drop quickly. If it’s getting too low, wait to resume exercising until your blood sugars stabilize. If you feel the symptoms of hypoglycemia, check your blood sugar and eat 15-20 grams of fast-acting carbs to quickly raise your blood sugars. Some examples:
- 4 glucose tablets (4 grams per tablet)
- 1 glucose gel tube (15 grams per gel tube)
- 4 ounces (1/2 cup or 118 mL) of juice or regular soda (not diet soda)
- 1 tablespoon (15 mL) of sugar or honey
- 5 lifesaver candies
Check your glucose levels again after 15 minutes. If it's still too low, have another 15 grams of carbs and wait. Repeat this every 15 minutes.
There is some evidence that men are at a greater risk than women for hypoglycemia during or after weightlifting or resistance exercise, but by checking your glucose before, during, and after exercising, you can help prevent hypoglycemia.
Helpful tech and guidelines for exercise
Activity monitors and devices can significantly help with diabetes management while exercising. Connected pens and insulin pumps provide timely dosage, continuous glucose monitors (CGM) let you follow trends to guide your insulin dosing and carb intake, and AID systems can help protect you from hypoglycemia and hyperglycemia.
Dr. Lori Laffel, chief of the pediatric, adolescent, and young adult section at Joslin Diabetes Center, provided a few basic guidelines if you’re engaging in aerobic exercise for more than 40 minutes. If you’re on multiple daily injections (MDI) or an open-loop pump, consider the following insulin adjustments:
- For those on MDI, start with a 20% reduction in basal insulin dose.
- For people on insulin pump therapy, use activity mode or reduce basal rate by about 50% (as a starting point) 1-2 hours before, during, and about one hour after exercise.
- Reduce bolus insulin by 50% for meals or snacks two hours before and up to two hours after exercise.
- At bedtime (or 7-11 hours following afternoon exercise), reduce your basal rate by 20% for up to six hours.
- If you are engaging in unplanned aerobic exercise, eat a few extra carbs.
- Use a CGM or glucose monitor to check glucose before, during, and after physical activity.
Everybody is unique and will respond to stress and exercise differently. It can be helpful to start an exercise log to figure out how your body responds to different exercises. Starting small by recording what time you exercise, your blood sugar before and after, and the general type of activity (i.e. aerobic, anaerobic, or both).
The bottom line
Making small but manageable changes in your daily activities will lead to improvements in your overall health and dramatically increase the likelihood that your new habits will be sustainable.
As a general rule of thumb, aerobic activity tends to lower blood glucose levels, and anaerobic activity tends to raise blood glucose levels. Actual effects of exercise on blood glucose levels can vary based on the person, type of activity, time of day, when (and how much) food was last eaten, and if there is any insulin in your system.
The best time to exercise is when you can most consistently make it happen – any type of movement is better than no movement. Remember to always check your glucose levels before and after physical activity and be prepared for hypoglycemia by carrying juice or glucose tablets with you when you exercise. Stop exercising if you feel lightheaded or have symptoms of hypoglycemia.
It’s important to always consult with a healthcare professional before you make any adjustments to your medications. Be sure to talk with your doctor or healthcare provider before you make any major changes to your exercise or activity routine.
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