Active people living with diabetes love the flexibility and finite control that using an insulin pump provides. Life no longer revolves around timed snacks and meals. Long-acting insulin peaks no longer control you. Even exercise participation can become spontaneous again. Whether you are new to pumping or a veteran, there are things to consider when you manage exercise blood sugars.
What Your Body Does With Glucose During Exercise
Understanding the non-diabetic body’s response to exercise can make exercise sessions on a pump a little smoother. As exercise starts, the body quickly begins to use glucose for fuel. This initial uptake of glucose must have some basal insulin available to occur, because the body immediately begins to use additional fuels and uses more blood glucose as a result. Although glucose uptake does not directly require insulin during exercise, the body needs some basal insulin to prevent excessive increases in hormones that raise blood sugars. As exercise continues and blood glucose levels begin to fall, there is a further drop in circulating insulin levels, and an increase in resistance. Glucose can continue, however, to enter cells in large amounts without the need for insulin, mainly through different pathways.
Matching the Need for Insulin
Those of us with insulin-dependent diabetes have the difficult task of “matching” the drop in insulin levels that comes from exercise. A pre-workout decrease in insulin level that is too early or too drastic may cause a rise in blood sugar related to exercise. A decrease that is too little or too late will result in hypoglycemia.
Amazingly, the body has many ways to ensure that glucose levels remain adequate, including drawing reinforcements from stored sources like liver and muscle and also using fat for energy. The greater the intensity of exercise, the greater the immediate draw for glucose from blood, liver and muscle stores, and the greater the production of lactic acid. Certain modes of exercise, particularly anaerobic types-short bursts of high intensity activity like sprinting or hockey-yield much higher lactic acid levels post-activity. Pattern your blood sugars and learn what is the usual response for you. A different type, intensity, or duration of exercise may change things, requiring a different blood sugar management strategy. Frequent regular exercise will serve to decrease carohydrate use and moderate many of the effects that throw off control.
The Pump vs. MDI
Multiple Daily Injection (MDI) therapy, which requires both long and short-acting insulin, generally means planning ahead for dosage adjustments prior to exercise. Using insulin pump therapy means an escape from long-acting insulins, offering users a number of ways to instantly control basal insulin dosage. Among other things, pump users can temporarily lower the basal rate, stop insulin flow with the suspend mode, and even completely disconnect from the pump. Instantaneous control of the basal rate more closely mimics the normal physiologic response to exercise, reducing both the need for pre-exercise snacks and the likelihood of exercise-induced hypoglycemia. Carbohydrate intake prior to exercise on MDI is often necessary to avoid hypoglycemia.
Some pump users may, however, experience post exercise hyperglycemia related to missed basal insulin, and the contribution to blood sugar by the lactic acid, liver and muscle glycogen that are produced by glucose-raising hormones. Varying the duration and degree of the basal rate reduction or ingesting a pre-exercise snack with a partial bolus can alleviate this.
People with diabetes and healthcare providers should be aware that ADA Clinical Practice Recommendations for Exercise (Jan. 2000) reflect minor revisions. The guidelines, which used to advise avoiding exercise when blood sugar levels are greater than 300 mg/dl, now say to “use caution” instead. This encourages more individualized modifications than previous recommendations. (See Table 1).
If the pre-exercise blood sugar is greater than 300, pump users must realize that hyperglycemia related to problems with pump mechanics-i.e. a clogged infusion set or site failure-will typically not normalize with exercise. In this case blood sugar may rise with exercise and possibly hasten ketoacidosis. Exercise is never a wise choice when ketones are present.
When correcting for a high or covering a meal or snack immediately prior to exercise, bolus conservatively. Exercise increases insulin sensitivity and hence your usual bolus, provided in proximity to exercise, may drop you faster and more severely than intended.
Understanding your own body’s response to the exercise you do is the key to managing blood sugars with exercise. Here’s wishing you successful pumping and the most enjoyable of exercise.