The Great Blood Glucose Balancing Act

Let’s take a look at aerobic and anaerobic activities in greater detail.

Aerobic activities
Most common activities, such as yardwork, cleaning, shopping, filing, playing, sex, and anything else that requires using your muscles for more than a few minutes, as well as aerobic exercise (activities performed at a moderate level for 20 minutes or more) will promote a blood glucose drop due to enhanced insulin sensitivity and accelerated glucose consumption by muscle cells. To prevent low blood glucose, a person can reduce his dose of insulin or other blood-glucose-lowering medicines, increase his carbohydrate intake, or do a combination of both.

When exercise is going to be performed within an hour or two after a meal, the best approach is usually to reduce your mealtime insulin or oral medicine. However, if you take insulin and plan to exercise at a time when you do not normally take rapid-acting insulin, it may work better to consume some extra carbohydrate before the activity. For activities lasting less than two hours, it is only necessary to reduce your dose of rapid-acting insulin. It is not usually helpful to reduce your intermediate-acting or long-acting insulin unless your activity is going to last more than two hours.

When adjusting mealtime insulin doses for exercise, both the dose you take to cover the food and any additional units you take to “correct” a high blood glucose reading need to be reduced. To accomplish this, I like to use an “activity multiplier.” Essentially, this means that you calculate your mealtime insulin dose as usual (based on the food you plan to eat and your current blood glucose level), then multiply the dose by a number that results in a lower dose. (For specific multipliers, see “Adjusting Premeal Insulin for Activity”.)

For example, if I take a leisurely 20-minute bike ride after dinner (which I consider a low-intensity activity), I multiply my dinner insulin dose by 0.90, which reduces the dose by 10%. If I plan a much more intense 90-minute ride up and down hills (which I consider a high-intensity activity), I would multiply my dinner dose by 0.50, which reduces my dose by 50%.

What about Anthony, whose wife likes to take him out for those 45-minute, moderate-intensity walks? If Anthony takes rapid-acting insulin at dinner, he should try multiplying his usual dose by 0.67, which will reduce it by 33%. Not only will this help him avoid hypoglycemia, but it will also enable him to lose more weight since excess insulin tends to promote weight gain.

If Anthony took oral medicines for his diabetes, he might need to reduce or eliminate the dose. Only certain drugs can cause hypoglycemia. Those that do not have the potential to cause hypoglycemia should not be changed.
Medicines that can cause hypoglycemia include the following:

• Glimepiride (Amaryl)
• Glipizide (Glucotrol, Glucotrol XL)
• Glyburide (DiaBeta, Glynase, Micronase)
• Insulin
• Nateglinide (Starlix)
• Repaglinide (Prandin)
• Combination pills that contain any of the above medicines

Medicines that do not cause hypoglycemia include the following:

• Acarbose (Precose)
• Exenatide (Byetta)
• Miglitol (Glyset)
• Metformin (Glucophage, Glucophage XR)
• Pioglitazone (Actos)
• Rosiglitazone (Avandia)

If you take a medicine that can cause hypoglycemia, it is usually recommended that you take your usual dose with your first couple of exercise sessions and see what happens. If your blood glucose drops below 80 mg/dl during or after exercise, reducing or eliminating the medicine might be in your best interest. Check with your doctor before making this type of change on your own.