Question: I went for a 23-minute walk outside, covering 1.3 km with an average heart rate of 123 bpm. Before the walk, my blood glucose was 4.3 mmol/L, and after, it rose to 5.4 mmol/L. I thought exercise would lower my blood glucose. Why did it increase?

Answer: This experience is common among people managing their blood glucose levels through exercise. While physical activity generally helps lower glucose over time, it can sometimes cause a temporary increase. This response is due to a process called the “fight-or-flight” response, where the body releases stress hormones, particularly cortisol and adrenaline, in response to the physical demand. These hormones signal the liver to release more glucose into the bloodstream, giving muscles the energy they need to perform during exercise (Dela, 2019).

Exercise intensity plays a role, too. Higher-intensity activities—like brisk walking at a heart rate around 120 bpm—require more fuel, which may prompt the liver to release stored glucose for quick energy. In individuals with insulin resistance or diabetes, this response can cause noticeable post-exercise glucose spikes (Kelley, 2020).

Interestingly, this initial spike usually normalizes over time. Regular exercise improves insulin sensitivity, which helps reduce baseline glucose levels. Walking at a lower intensity may help you avoid these spikes if that is your goal. However, even if glucose levels rise temporarily, the long-term benefits of exercise on glucose management are well-documented.

Sources:

• Dela, F. (2019). The Physiology of Glucose Regulation During Exercise. Journal of Applied Physiology.
• Kelley, D. E. (2020). Managing Blood Glucose with Exercise: The Role of Insulin Sensitivity. Diabetes Care.