In managing your diabetes,
Overall, we think of exercise as reducing blood sugars but is not s straight forward as it sounds. Your hormones can have a big impact on your exercise.
Hormones and Exercise
The human body only has insulin to lower sugars but has five hormones that raise it. Why the redundancy? From a survival standpoint, your body wants to make sure you do not run out of sugar. Insulin is an important hormone for regulating your body’s storage of fuels (carbohydrate, fat, and protein) after you eat. It tells your insulin-sensitive cells (mainly your muscle and fat cells but also your liver) to take up glucose and fat to store them for later use.
During exercise, any insulin in your bloodstream can make your muscles take up extra blood glucose. In people who have a pancreas that functions normally, insulin levels typically decrease during exercise, and levels of a hormone called glucagon (released from the alpha cells of the pancreas) rise to stimulate glucose (sugar) release.
Your blood sugar levels are managed by your liver, which would normally respond to the relative amounts of insulin and glucagon. After a meal, insulin and glucagon tell the liver to store sugar. Fasting overnight or doing extended exercise leads to glucagon signaling the liver to release glucose.

People with type 1 diabetes or type 2 that use insulin, respond hormonally to exercise. Thee level of insulin and glucagon in the liver are seldom normal because their insulin is injected or pumped under the skin rather than released directly from the pancreas. People with type 1 diabetes have an altered hormonal response to exercise when their peripheral insulin is relatively high; lowering the circulating level of insulin helps normalize their hormone response.
All exercise causes the release of hormones that increase the production of sugar by the liver and lower your muscular use, depending on how long and hard you exercise. Easy and moderate activities only release a small amount of glucose-raising hormones as long as is done for short duration of time.
Intense exercise such as heavy resistance training, sprinting, or high-intensity intervals causes an immediate rise in your blood glucose and leads to an exaggerated release of hormones. These hormones include adrenaline (formally known as epinephrine) and norepinephrine, which are released to allow your body to respond to physical or mental stressors with an increased heart rate. Glucagon, growth hormone, and cortisol are also release.
The effects of these glucose-raising hormones can easily exceed your body’s immediate need for sugar especially since high-intensity exercise may not last long.
Blood sugar often increase during and after short bouts of intense activity. In fact, you should expect intense exercise potentially to cause a large increase in blood sugar because of your body’s exaggerated release of glucose-raising hormones such as adrenaline and glucagon.
What does That Mean for Patients Who Use Insulin and Exercise?

You may be more insulin resistant immediately after intense exercise and for a few hours due to these hormones. In one study, after high intensity exercise, one group of people with type 1 diabetes on insulin pumps experienced elevated blood glucose levels for nearly 2 hours. Similarly, in exercisers with type 2 diabetes, blood sugar also rose for 1 hour in response to high intensity exercise, as did their insulin levels (because their bodies still produced their own insulin).
You may need some supplemental insulin to bring your blood glucose back to normal (albeit less than normal), or it may drop slowly over time on its own. After these hormones wane, your blood sugar may easily drop later when your body is working hard to restore the sugar your muscles used during the activity. Be on the lookout for later-onset lows in these cases.
Overall exercise will lead to lower blood sugars in patients with diabetes. However, those patients who use insulin will need to be careful when doing high-intensity exercise as this can lead to an increase in blood sugars right after exercise. For exercise, in general, be on the lookout for low blood sugars but when they happen will depend on the type, duration
References:
- Excerpted from Colberg, SR, Chapter 2, “Balancing Exercise Blood Glucose” in The Athlete’s Guide to Diabetes: Expert Advice for 165 Sports and Activities. Champaign, IL: Human Kinetics, 2019.