Physical Activity: Warnings and Safeguards

Your health care team can help you plan your meals, snacks and when to take your medication based on the type of physical activity you do.

If you have been living with diabetes for several years and have such chronic diabetes complications as heart, neurological or other problems have begun to appear, or if you have been sedentary for many years, consult your doctor before starting any exercise program more intense than brisk walking.

Before you begin

Before embarking on a physical activity program, it is recommended that you have a complete medical checkup (blood pressure, cholesterol levels in the blood, glycated hemoglobin (A1C) and glycemia, heart and circulatory system, kidney function, eye and feet health). This checkup will help identify the most appropriate type of physical activity for you.

Contra-indications (unless directed otherwise by your physician): cardiovascular problems can make certain high-intensity activities unsafe.

Your doctor can also advise you as to the best time of day to do physical activity based on your type of medication and when you take it. He can also adjust our insulin dosage based on the type of physical activity you do.

Some tips when doing physical activity:

  • Listen to your body and stop if you feel unwell.
  • Stay hydrated by drinking regularly.
  • Make sure you have identification on you (e.g.: bracelet, medallion or card) that indicates that you are diabetic.
  • Wear appropriate shoes and socks.
  • Inspect your feet carefully before and after exercise to detect any blisters or other wounds.
  • Talk to your doctor if any of the following symptoms occur when exercising: nausea, fainting, severe fatigue, headache, blurred vision, dizziness, shortness of breath.

Don’t hesitate to ask for advice from an exercise professional, like a kinesiologist.

Physical activity and hypoglycemia

Physical activity increases glucose use by the muscles and sensitivity to insulin. Consequently, there is a risk of hypoglycemia during and after exercise (up to 48 h), primarily for people with type 1 diabetes or for people with type 2 who take insulin or a drug that increases insulin secretion (gliclazide (Diamicron®and Diamicron MR®), glimepiride (Amaryl®), glyburide (Diabeta®), repaglinide (GlucoNorm®)).

To prevent hypoglycemia:

  • Monitor your blood glucose (sugar) levels before and after exercising to anticipate a hypoglycemic episode. If the activity lasts 60 minutes or more, take another reading midway through the session.
  • Continue to monitor your blood glucose (sugar) levels closely for up to 48 hours after the activity, especially if the activity was prolonged.
  • Always carry a supply of concentrated sugar, such as glucose tablets or a regular soft drink, in case of hypoglycemia.

Your health care team can help you plan your meals, snacks and when to take your medication based on the type of physical activity you do.

If your blood glucose (sugar) reading is less than 4 mmol/L, treat the hypoglycemia before starting to exercise.

Guide to supplemental carbohydrates during exercise

Type of physical activityBlood sugar (mmol/L)Supplemental carbohydrates
Short duration (less than 30 minutes) at low intensity< or = 5.510 to 15 g
> 5.5Not necessary
Medium duration (30 to 60 minutes) at moderate intensity< ou = 5.530 to 45 g
5.5 to 9.915 g per 30 to 45 minutes of exercise
10.0 to 13.9Not necessary
Long duration (more than 60 minutes) at high intensity< or = 5.545 g
5.5 to 9.930 to 45 g
> 9.915 g per hour

Source: CHUM Hotel-Dieu Metabolic Medecin Day-Care Centre, 2013, Understand Your Diabetes and Live a Healthy Life, page 194.

For a handy guide to exercise, blood glucose (sugar) levels and snacks, get a copy of the Roulette de l’activité physique (French only).

If you have type 1 diabetes

Here are a few extra strategies to help you avoid hypoglycemia during exercise:

  • Don’t exercise on an empty stomach (fasting) and avoid delaying your meals.
  • Do very short intervals (10 seconds) at maximum intensity at the beginning or end of a moderate-intensity exercise session.
  • Do your strength/weight training exercises immediately before your aerobic exercises (Canadian Diabetes Association, 2013).
  • Avoid injecting insulin in an area of your body that will be worked during the activity (for example, do not inject into your arm if you intend to play tennis). That would accelerate insulin absorption and could cause hypoglycemia.

Physical activity and hyperglycemia

During and after nearly all types of exercise, blood sugar levels tend to drop, since the cells are more sensitive to insulin. However, a short-duration, but very intense physical activity (shovelling snow, playing hockey or basketball) can cause transient hyperglycemia because the body will produce more glucose than it uses due to the activation of stress hormones.

If you are in a hyperglycemia state before you start, physical activity could make it worse. Therefore, it is prudent to monitor your blood glucose (sugar) levels more often if you start doing physical activity when in a state of hyperglycemia.

Elevated glycemia can be due to:

  • dehydration, which increase the concentration of glucose (sugar) in the blood
  • stress hormones, such as adrenalin, secreted during high-intensity exercise (more glucose is produced by the liver than is used by the muscles)

Be sure to hydrate before and during the activity to avoid increasing the concentration of glucose (sugar) in the blood when you lose water through sweat, especially on hot, humid days.

Advice if you have type 1 diabetes:

If your blood glucose (sugar) level is higher than 16.7 mmol/L and you don’t feel well, measure the ketones in your blood or urine.

  • If ketone levels are high, all vigorous activity should be postponed and the hyperglycemia treated as per your doctor’s instructions.
  • If ketone levels are normal and you feel OK, there is no reason to postpone the physical activity.

Advice if you have type 2 diabetes:

It is generally unnecessary to postpone an exercise session, as long as you feel OK.

However, if your blood glucose (sugar) level is higher than 16.7 mmol/L, it is important to stay well hydrated and watch for the signs and symptoms of hyperglycemia, including increased thirst, nausea, severe fatigue, blurred vision or headache.

Research and text: Diabetes Québec Team of Health Care Professionals

Scientific review: Cathy Dresdell, M.Sc., Kinesiologist

June 2014 (updated on July 2018)

©All rights reserved Diabetes Quebec

References:

CHUM Hotel-Dieu Metabolic Medecin Day-Care Centre, 2013, Understand Your Diabetes and Live a Healthy Life.  Montreal: Les Éditions Rogers limitée. Available in the store.

Sigal R, Armstrong M, Bacon S et al. Diabetes Canada 2018 Clinical Practice Guidelines for the Prevention and Management of Diabetes in Canada: Physical Activity and Diabetes. Can J Diabetes 2018; 42 (Suppl 1): S54-S63.