July 27, 2000
Exercise and Sports, Insulin Pumps
Question from Madison, Wisconsin, USA:
I am in a quandary about how to effectively deal with post-exercise highs in blood glucose readings. I am curious as to your ideas for eliminating these rises. My question is two-fold. First, what causes precipitous rises in blood glucose readings after exercise, even if readings are in the normal range, 80-130 mg/dl (4.4-7.2 mmol/dl) before exercise? Second, I am 34 years old and have had type 1 diabetes since I was eight years old. I am currently using a pump. I jog between 30-60 minutes a day, five days a week. My blood glucose readings routinely spike 100 mg/dl (5.6 mmol/dl), or more, after exercise (this occurs regardless of if blood glucose is in a normal range or not before exercise) and stay elevated for up to eight hours. The magnitude of these rises does not seem correlated to duration or intensity of exercise. To lower these readings, I have tried using an increased temporary basal rate (up to 0.3 units per more for up to four hours post-exercise), an increased basal during exercise, and have also tried using a corrective bolus dose after exercise, none of which is particularly effective. What measures can you suggest to avoid these post-exercise rises in blood glucose?
It is difficult to say exactly what is going on in your situation but you are certainly not alone with regards to your observations. Pump users, in particular, often observe rises in blood sugar related to exercise. This occurs for a number of reasons, the greatest contributions being the mobilization of liver and muscle glycogen in response to the increased need for glucose during exercise; and the conversion of lactic acid to glucose during and particularly post exercise. Recall that lactic acid is a metabolic end product produced in greatest amount in response to “anaerobic” or higher intensity/power-type activities. The body converts lactic acid to glucose, which is used to replenish glucose stores. On multiple injection programs, the rise in blood sugar related to these issues is typically “hidden” under an umbrella of longer acting insulin. On a pump, however, the more exact nature of insulin delivery allows us to see this.
The measures which you have mentioned are all excellent, and some pumpers find that one or the other works best for them. I have some specific questions and related suggestions for you regarding the current management of basal rates during exercise:
Are you confident that your current basal rates are correct without exercise? If you have not recently verified your rates via basal rate testing, it may be extremely valuable to do so, particularly in the time frame that you are having difficulty.
Where are you exercising in relation to the previous meal? Consider the effect of the meal, and in particular, the effect of protein intake 4-6 hours previous on glycemic control.
Do you decrease your basal rates before, during or after exercise? Do you suspend or disconnect your pump while exercising? For some, those delayed rises are related to missed or sub-optimal basal rates during exercise. This can be dealt with a number of ways, including replacing the missed basal (or a portion of) either prior to, halfway through or immediately after the exercise session depending on the blood sugar and the risk of hypoglycemia.
Lactic acid is produced in greater amount in activities of higher intensity, or activities which contain short bursts of anaerobic/power-type movements. Often a change in mode or intensity of exercise will have an effect. Do you see the same rise in blood sugar if you walk versus run? Not that I’m advocating changing what you enjoy doing, I’m simply curious as to your observed response.
One technique that some insulin pump users have used with success is to ingest a carbohydrate snack with a partial bolus (usually 50-60%) immediately prior to or during exercise. The snack provides a glucose source for immediate energy expenditure, while the bolus both prevents an excessive elevation and also appears to provide some additional circulating insulin that addresses the lactic acid and related rise in glucose levels post exercise.
I understand your frustration, but you should be commended for the great work you have done with patterning your blood sugar response to exercise. As you have already discovered, it may take a bit of trial and error but you will find a technique that works for you!