Why Does Exercises Sometimes Raise Blood Sugar?

Learn why certain types of exercise spike blood glucose.

Have you ever noticed that your blood sugar lowers after some types of exercise, while your blood sugar rises after other kinds of exercise? 

Most aerobic exercise (or cardio) will lower your blood sugar levels, while activities like resistance training or high-intensity training may raise your blood sugar. People with type 1 diabetes, LADA, or another insulin-dependent form of diabetes are most likely to notice more significant changes in their blood sugar levels from exercise. 

When not expected, seeing blood sugar levels rise after exercise can be frustrating, especially because you’re taking steps to improve your health.

Learn the science behind why some exercises raise blood sugar, what you can do to counter blood sugar spikes from exercise, and the long-term effects of exercise on blood sugar.

Why Does Exercise Raise Blood Sugar?

When you do high-intensity exercises, such as strength training, weightlifting, high-intensity cardio, or high-intensity interval training (HIIT), your body releases hormones that help your body perform these activities.

These types of exercise differ from moderate exercises, such as brisk walking or biking, as your body typically doesn’t require the release of additional hormones to complete these exercises. 

Hormones such as adrenalin, cortisol, and glucagon all increase blood sugar. The hormone insulin lowers blood sugar. When you have diabetes, your body either doesn’t make insulin or makes very little insulin (type 1 diabetes and LADA), or you are insulin resistant (type 2 diabetes and prediabetes). Because of this, people with diabetes will notice these hormones have a more significant effect on their blood sugar levels than people without diabetes.

In an interview with DiabetesMine, professor Sheri Colberg, Ph.D., and creator of diabetesmotion.com, explained, “It’s critical for your brain and your nervous system to have access to blood glucose at all times. For that reason, the body has redundant hormones that raise blood glucose, like glucagon and adrenaline. What happens with exercise is that glucose-raising hormones are released to help pump up the amount of blood glucose being released to match what your active muscles are using.”


Adrenaline is released when your body is under stress. Often referred to as the “fight or flight hormone,” adrenaline works with cortisol to raise blood sugar. Adrenaline inhibits insulin release, which increases your blood sugar levels since insulin is the only hormone that lowers blood sugar.

Your body releases adrenaline during periods of intense exercise. Typically this hormone isn’t released during moderate exercise unless it exceeds 2 hours. Adrenaline instructs your liver to release stored glucose in the form of glycogen. This glycogen provides your body with the extra fuel it needs during intense exercise.

Adrenaline levels typically return to normal shortly after exercising.


Cortisol is commonly referred to as the “stress hormone” because cortisol levels rise when your body is subjected to physical, environmental, or psychological stress. It makes muscle and fat cells resistant to insulin while enhancing glucose production by the liver. During periods of intense exercise, cortisol can cause large spikes in blood sugar.

Types of Exercise That Raise Blood Sugar

Exercise can be split into two categories: aerobic and anaerobic. Aerobic exercise is what most people think of when they think of cardio exercises. Activities such as aerobics, walking, running, biking, dancing, and swimming are all aerobic exercises. Aerobic exercises are activities that can be sustained for extended periods of time.

Conversely, anaerobic exercises are not sustainable. These exercises are done in short “bursts” and include activities such as sprinting, resistance training, weight lifting, and high-intensity interval training (HIIT).

Both types of exercise are important for overall wellness, and both positively affect blood sugar over the long term.

Resistance Training

Sometimes referred to as strength training, resistance training is one of the best things you can do for your body. Resistance training can mean lifting weights at a gym or at home or can be achieved using resistance bands or bodyweight.

Benefits of resistance training include:

  • Build strength
  • Improve mobility
  • Improve insulin sensitivity
  • Lose weight
  • Lower your risk for heart disease

Resistance training is a form of anaerobic exercise, so it’s important to be mindful of your blood sugar levels when exercising. For most people with diabetes, resistance training will temporarily raise blood sugar levels during exercise and for a short period after exercise.

The safe range for exercise when you have diabetes is greater than 100mg/dL and less than 250mg/dL.

How To Counter Blood Sugar Spikes From Exercise

There is no one-size-fits-all solution to counter blood sugar spikes. For people with type 1 diabetes or insulin-dependent LADA, you will need to adjust your insulin intake to account for blood sugar spikes.

Because everyone responds to exercise and insulin differently, the best way to do this is to see how your body responds to exercise and how your body responds to the type of insulin you take. Be sure to consult your doctor to determine a plan for adjusting your insulin during exercise.

Some blood sugar spikes will be unexpected from a burst of adrenaline during the middle of your workout. In this scenario, you may need to adjust after the fact rather than try to anticipate spikes. 

Wearing a continuous glucose monitor (CGM) is one of the best ways to monitor your blood sugar levels during exercise. Your CGM will give you a close to a real-time reading of your blood sugar levels and allow you to adjust your activity, insulin, and food intake as needed.

If you have prediabetes or type 2 diabetes, you will likely have less of a spike in your blood sugar as a result of exercise. This is because while you may be insulin resistant, your body still produces insulin. Most of the time, you’re not prescribed insulin when prediabetes or type 2 diabetes, so you have fewer options to counter blood sugar spikes from exercise.

Here are three tips from the American Diabetes Association to help keep blood sugar levels from rising during workouts:

  1. Practice relaxation techniques such as paced breathing, visualization, or meditation before and during your workout to minimize the adrenaline effect.
  2. Avoid eating excessive amounts of carbohydrates before and during your workouts. Instead, try some yogurt with nuts or peanut butter.
  3. Consider moving your workout to later in the day if you usually exercise in the early mornings. The dawn phenomenon, a natural rise in blood glucose that occurs between about 4:00 and 8:00 a.m., can result in higher levels during morning exercise. The same workout done later in the day is less likely to result in a rise.

Long-Term Effects of Exercise on Blood Sugar

Exercise increases insulin sensitivity. This means that your body is more receptive and responsive to the insulin you produce (or inject if you have type 1 diabetes and no longer produce insulin naturally). As a result, blood sugar levels are lowered for at least 24 hours after exercise. If you incorporate exercise into your daily routine, you will find your blood sugar is lower overall, and your HbA1c, which measures your average blood sugar over the past three months, will also be lower.

Even though you may see blood sugar spikes from intense anaerobic exercise, you will still find that your blood sugar levels will be lower overall. 

Research has found that regular exercise lowered HbA1c levels by 0.7 percentage points, regardless of any weight loss.

For people with prediabetes and type 2 diabetes, regular exercise is important when working towards reversing diabetes. While type 1 diabetes and LADA are permanent and not reversible, you will still see significant gains in your overall health, wellness, and blood sugar levels with regular exercise.

The Bottom Line

Exercise is an important part of overall health, and is especially important if you have diabetes. Regular exercise will lower blood sugar levels for up to 24 hours, improve insulin sensitivity, and make managing diabetes easier overall.

However, it is important to be aware that some types of exercise can temporarily raise blood sugar levels. This is usually temporary and may start during exercise and extend a few hours after exercise. Most often, this only occurs with intense physical activity such as resistance training, weight lifting, sprinting, HIIT (high-intensity interval training), or with moderate activity that lasts over 2 hours.

Always make sure your blood sugar is in a safe range before you begin exercising and be prepared to take any necessary corrective action if your blood sugar levels rise during or after exercise.