Before exercise, adjust the bolus or basal insulin, or both, in anticipation of the exercise.
• A bolus of a fast-acting insulin analog lasts for about four hours, and the peak is at about one to one and a half hours. If you exercise within two hours, you will need to cut back on the premeal bolus (to 50 to 75 percent of your usual dose).
• Making an adjustment in basal insulin dosing is easier if you are on an insulin pump. If you are planning for exercise of long duration (longer than ninety minutes), you may want to cut back the amount of your basal insulin for up to two hours before the exercise. If you are participating in competitive sports, you may find that the "adrenaline rush" means that you may have to increase your basal insulin temporarily for up to two hours before the exercise.
• Adjusting the basal dosage of the long-acting insulins like glargine or detemir is trickier—you can try cutting back to 50 to 80 percent of the dose on the days you exercise. Any high glucose levels earlier in the day can be covered by giving additional bolus insulin.
During exercise your options will depend whether you are on a pump or on injections.
• If you are on the pump, you have a number of options as to what to do regarding the basal insulin delivery. For short-duration exercise lasting an hour or so, you can simply come off the pump. If the pump is taken off for more than an hour (for example, while swimming), a small bolus may be given before coming off. If you will be exercising for several hours, a temporary basal amount (20 to 75 percent of your usual dose) might be necessary. For example, if you go cross-country skiing for several hours, you may change your basal to 20 to 50 percent of your usual dose for the duration of the exercise. A similar change may be required for a marathon.
• If you are on insulin glargine or detemir, you do not have the option of changing the basal rate during exercise: your only option is to consume additional carbohydrates.
After exercise you will adjust the bolus and basal insulins for the acute effects of exercise and also for the effects of chronic exercise.
• If you get predictably high glucose levels after exercise, be prepared to give a little bolus of a fast-acting insulin analog. With intense and/ or prolonged exercise, hypoglycemia can occur several hours (up to twelve to sixteen hours) afterward, and you should be prepared to reduce the basal insulin (or eat a snack). You might consider purchasing a continuous glucose monitoring system that can alert you to overnight hypoglycemia.
• After a weekend of increased physical activity such as skiing, a reduction in insulin requirements may persist for an additional twenty-four hours.
• With exercise training, you may become more insulin sensitive, and you may need to change your usual insulin regimen by cutting back on both basal and bolus insulin doses.
Was this article helpful?