Diabetes and exercise: When to monitor your blood sugar

Exercise is an important part of any diabetes treatment plan. To avoid potential problems, check your blood sugar before, during and after exercise.

By Mayo Clinic Staff

Diabetes and exercise go hand in hand, at least when it comes to managing your diabetes. Exercise can help you improve your blood sugar control, boost your overall fitness, and reduce your risk of heart disease and stroke.

But diabetes and exercise pose unique challenges, too. To exercise safely, it's crucial to track your blood sugar before, during and after physical activity. You'll learn how your body responds to exercise, which can help you prevent potentially dangerous blood sugar fluctuations.

Before exercise: Check your blood sugar before your workout

Before jumping into a fitness program, get your doctor's OK to exercise — especially if you've been inactive. Talk to your doctor about any activities you're contemplating, the best time to exercise and the potential impact of medications on your blood sugar as you become more active.

For the best health benefits, experts recommend at least 150 minutes a week of moderately intense physical activities such as:

  • Fast walking
  • Lap swimming
  • Bicycling

If you're taking insulin or medications that can cause low blood sugar (hypoglycemia), test your blood sugar 30 minutes before exercising.

Consider these general guidelines relative to your blood sugar level — measured in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L).

  • Lower than 100 mg/dL (5.6 mmol/L). Your blood sugar may be too low to exercise safely. Eat a small snack containing 15 to 30 grams of carbohydrates, such as fruit juice, fruit, crackers or even glucose tablets before you begin your workout.
  • 100 to 250 mg/dL (5.6 to 13.9 mmol/L). You're good to go. For most people, this is a safe pre-exercise blood sugar range.
  • 250 mg/dL (13.9 mmol/L) or higher. This is a caution zone — Your blood sugar may be too high to exercise safely. Before exercising, test your urine for ketones — substances made when your body breaks down fat for energy. The presence of ketones indicates that your body doesn't have enough insulin to control your blood sugar.

    If you exercise when you have a high level of ketones, you risk ketoacidosis — a serious complication of diabetes that needs immediate treatment. Instead, take measures to correct the high blood sugar levels and wait to exercise until your ketone test indicates an absence of ketones in your urine.

Dec. 01, 2015 See more In-depth