Predict your blood glucose response and make regimen changes. Based on the type of activity you do, time of day you exercise, and amount and timing of your insulin delivery, you can often predict the effect of exercise on your blood glucose level and make appropriate changes. Of paramount importance are the length and intensity of the exercise and your training level.
Establish your pattern. Each time you try a new activity, check your blood glucose level frequently (before, during, and several times after an activity) to establish your usual response to the exercise, as well as variations from your predicted response.
Learn from the past. Make regimen changes (increased carbohydrate consumption and/or decreased insulin) based on your previous blood glucose response to an activity. You may also make regimen changes based on whether physical fitness or weight loss is a goal of the exercise. If you want to train hard and frequently for fitness, you will have to eat to replace the calories you are using. If weight loss is your goal, you may want to lower your insulin doses (instead of snacking) to maintain blood glucose control.
Prevent hypoglycemia. Learn to adjust your insulin doses to prevent hypoglycemia from occurring during exercise and for up to 24 hours afterward. Consider leaving your basal rate lowered for a longer period of time following more strenuous or prolonged activities.
Expect a training response. Once you have been doing an activity consistently for two to three weeks, you will experience a training response that will alter your blood glucose usage. Training increases your capacity for fat utilization, which has the potential effect of sparing blood glucose. For prolonged aerobic activities, training may result in your blood glucose level dropping less during an activity, resulting in the need for smaller regimen changes. In addition, as your muscle mass increases in response to training, your overall insulin sensitivity may increase, lowering your basal and bolus insulin needs.
Recommended regimen changes
The American College of Sports Medicine (ACSM) and the American Diabetes Association (ADA) have established general clinical practice recommendations for exercise and diabetes that apply to insulin pump users as well. According to these guidelines, people with diabetes should avoid exercising if their fasting blood glucose level before exercise is above 250 mg/dl and there is an elevated level of ketones present in the blood or urine. A blood glucose level above 300 mg/dl with no ketones indicates the need for “caution.” A third guideline is to ingest some carbohydrate if one’s blood glucose level before exercise is below 100 mg/dl.
The problem with these recommendations is their generality, so before beginning an exercise regimen, talk with your health-care provider about what you personally should do in these situations. It is a good idea for all people with diabetes to check their preexercise blood glucose level. However, contrary to the ACSM and ADA guidelines, pump users with a blood glucose level below 100 mg/dl before exercise may not require a carbohydrate snack since they can simply reduce or suspend basal insulin during an activity.
The insulin reductions and/or carbohydrate intake you require for aerobic activities will depend on the intensity and duration of your activity. You should be able to compensate for shorter, less intense activities with a change in either your insulin (basal and/or bolus doses) or carbohydrate intake. For short, intense activities such as weight training, you may not require any immediate regimen changes, but you will need to anticipate and prevent delayed-onset hypoglycemia from occurring later on. For longer, more intense exercise, you will generally require a combination of carbohydrate intake (15-60 grams per hour) and insulin reductions (25%-100%) to maintain normal blood glucose levels.