Why Does Your Blood Sugar Sometimes Increase After a Walk or Workout? Doctor Explains The Surprising Reason

Exercise is generally recommended to help manage blood sugar levels, particularly in people living with diabetes. Walking, cycling, swimming, and strength training can help muscles use glucose for energy and improve insulin sensitivity. However, some people notice something unexpected when they check their glucose levels after a workout: their blood sugar has increased instead of dropping.

“While this may seem confusing, a temporary rise in blood sugar after physical activity is not always a cause for concern. The body's response depends on the type, intensity, and duration of exercise, as well as insulin levels and existing glucose control,” shares Dr Himika Chawla, Endocrinology & Diabetology at PSRI Hospital, Delhi.

Why Can Blood Sugar Increase After Exercise?

According to the American Diabetes Association, one of the main reasons blood sugar rises during or immediately after exercise is the release of stress hormones, particularly adrenaline and cortisol.

During physical activity, the body needs additional energy to support working muscles. To meet this demand, the liver releases stored glucose into the bloodstream. It can also produce new glucose to ensure that the body has enough fuel.

At the same time, hormones such as adrenaline signal the liver to release more glucose. During intense exercise, this glucose release can temporarily exceed the amount being used by the muscles, resulting in a rise in blood sugar.

This response is more common during high-intensity workouts, heavy weightlifting, sprinting, and other strenuous activities than during gentle walking.

High-Intensity Exercise Can Trigger A Glucose Spike

Not all forms of exercise affect blood sugar in the same way.

Moderate activities, such as brisk walking, cycling, and swimming, generally help muscles absorb glucose from the bloodstream. This can lower blood sugar levels.

However, intense workouts can trigger a temporary increase because the body releases adrenaline and other counter-regulatory hormones. These hormones stimulate the liver to release glucose to meet the body's increased energy requirements.

For instance, someone may notice a higher glucose reading after sprinting, high-intensity interval training (HIIT), or heavy resistance training.

This does not necessarily mean the exercise is harming blood sugar control. The rise may settle once the body recovers.

Also Read: Just Four Minutes of Exercise a Day May Help Control Blood Sugar, Study Finds

The Liver Releases Stored Glucose During Physical Activity

The liver plays an important role in maintaining blood glucose levels, particularly during exercise.

According to a case study-based research article published in the journal ‘PLOS One’, when muscles need more energy, the liver breaks down stored glycogen into glucose and releases it into the bloodstream. This process is known as glycogenolysis.

• The liver may also produce glucose through a process called gluconeogenesis.
• These mechanisms help prevent blood sugar from falling too low during physical activity.

However, in people with diabetes, particularly those with insufficient insulin availability or insulin resistance, the glucose released by the liver may not be used efficiently by the body.

As a result, blood sugar levels may temporarily increase during or after exercise.

Morning Workouts May Cause Higher Blood Sugar

Some people notice higher glucose readings when they exercise early in the morning. 

This may be linked to the dawn phenomenon, a natural rise in blood sugar that occurs in the early morning hours due to hormonal changes.

Hormones such as cortisol and growth hormone signal the liver to release glucose, helping the body prepare for the day. If someone exercises during this period, the additional hormonal response to physical activity may contribute to a further rise in blood sugar.

However, the response varies from person to person and depends on their diabetes management and insulin levels.

Dehydration Can Also Affect Blood Sugar Readings

Not drinking enough water before or during exercise can contribute to higher blood sugar concentrations.

When the body loses fluids through sweating without adequate replacement, blood volume decreases. This can make glucose levels appear more concentrated in the bloodstream.

Dehydration can also increase physical stress on the body and make blood sugar management more difficult.

Therefore, maintaining adequate hydration is important, particularly during prolonged workouts or physical activity in hot weather.

Also Read: Walking On Treadmill VS Walking Outdoors: What Is Best For Your Health?

Exercising With High Blood Sugar Can Sometimes Make It Worse

People with diabetes should also consider their blood sugar levels before starting a workout.

When insulin levels are insufficient, particularly in people with type 1 diabetes, intense exercise can further increase blood glucose because stress hormones stimulate the liver to release more glucose.

If blood sugar is very high and ketones are present, exercising can be dangerous and may increase the risk of diabetic ketoacidosis (DKA), a serious complication that requires urgent medical attention.

People with diabetes should follow their doctor's advice on checking glucose and ketones before exercising, especially when their readings are unusually high.

How Can You Prevent Blood Sugar Spikes After Exercise?

A temporary increase in glucose does not mean you should stop exercising. Instead, understanding how your body responds to different activities can help you make appropriate adjustments.

Here are a few things to keep in mind:

• Choose moderate activities: Brisk walking, cycling, and swimming may help improve glucose utilisation.
• Stay hydrated: Drink enough water before, during, and after exercise.
• Monitor blood sugar: Check glucose levels before and after workouts to understand individual patterns.
• Avoid sudden intense workouts: Gradually increase exercise intensity and duration.
• Follow medical advice: People taking insulin or medicines that can cause hypoglycaemia may need adjustments to their exercise and medication plans.

When Should You Be Concerned?

An occasional, temporary rise in blood sugar after exercise is not necessarily harmful. However, consistently high readings, particularly when accompanied by excessive thirst, frequent urination, nausea, or unusual fatigue, should not be ignored.

People with diabetes should discuss recurring post-exercise glucose spikes with their healthcare provider to understand whether changes in medication, meal timing, or workout intensity are needed.

Final Word

Experts emphasise that exercise does not always cause an immediate drop in blood sugar. While muscles generally use more glucose during physical activity, the liver and stress hormones also influence glucose levels. Understanding this balance can help people exercise safely and manage their blood sugar more effectively.