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March 16, 2003

Exercise and Sports

Question from DeKalb City, Georgia, USA:

My 15 year old daughter, who has had type 1 diabetes for about five months, has an A1c of 6.2% which pleases her health care team very much, and she has been swimming all year round since she was nine (currently six days per week, three hours per day) in addition to running, weights, etc. However, she seems to be having trouble controlling her sugar well at meets, so she can swim optimally. The standard meals are not normally timed, and there is the adrenalin issue. Her health care providers really do not have that specialized knowledge.as to the specifics of carbs, insulin, and time in relation to her racing. I have very controlled type 1 diabetes, so she and I are trying together to formulate a plan for meets. She normally uses 28 units of Lantus in the evening with 10 units of NovoLog before dinner, but we are trying to adjust for high and low sugars right before she races, as she sees the results of either in her times. We have tried locally to find another competitive swimmer at her level of practice but have failed, and she is not ready to discuss the pump yet. Can anyone help us with these highly specific questions? She does not want to quit competitive swimming.


I am sure that you and your daughter are very proud of her accomplishments! Your questions are thoughtful, thought-provoking, and reasonable.

I am not certain that an insulin pump will be the answer since she will not be wearing it during all those swim practices and meets! (You probably know that Olympian swimmer Gary Hall has Type 1 diabetes also.) So, I think that Lantus (insulin glargine) and NovoLog are very good choices.

I presume that you have experimented with different insulin doses and snacks before meets and practices. I am not certain that this forum allows any degree of specific advice. Does she “bottom out” after swimming? What glucose level does she find is “the best” for her competition and practices? Given that excellent hemoglobin A1c and her on-going exercising, I think I would cautiously advise that she find a glucose that allows her to “feel right” during her meets and then adjust the meals and insulin to meet that. In a gross generalization, I would be willing to consider foregoing (too much) insulin on competition days — recognizing that her own adrenalin and cortisol rushes will push her glucose up, but the swimming will bring her down. If she finds that she is particularly high (or even has urine ketones), then a little “nudge of NovoLog” may be very appropriate but I’d consider a formula such as: Current blood sugar minus target blood sugar (example 150) and then divide the number derived by her “sensitivity factor.”

There are several tools that people use to determine one’s “sensitivity factor” but essentially it is the amount of glucose that falls after she gets 1 unit of rapid-acting insulin. So, if for example, 1 unit tends to drop her by 100 mg/dl [5.6 mmol/L] (during a swim day), and her current glucose level was 380 mg/dl [21.1 mmol/L], then 380-150 divided by 100 would be 2.3. I would round down on swim dates to “2” such that for the example given, she might take 2 units of her NovoLog.

No doubt you will need to experiment, certainly discuss any plan with your daughter’s diabetes team, and I would not employ this strategy for the first time during a competition!

Additional comments from Delaine M. Wright, Clinical Exercise Physiologist:

Blood sugar response to exercise can vary significantly depending on whether the activity is “anaerobic” (high intensity, all-out shorter bursts of power/speed such as swim sprints, power weight training), or “aerobic” (such as endurance or distance training). In addition, and unfortunately as you have already indicated, the anxiety of competition may push pre-exercise blood sugars up rather dramatically and quite different from the control you may have accomplished during daily training. In general, even athletes without diabetes experience this pre-competition adrenaline-driven elevation in blood sugar level prior to a race.

Attempting to control an excessive rise is possible with a small amount of rapid acting insulin, but it should be done cautiously as it will increase the risk of low blood sugar during exercise. Most athletes with diabetes note that the adrenaline-induced highs generally come down with exercise. However, hypoglycemia during exercise will immediately drain the body of energy and put the athlete at risk for loss of consciousness. The Diabetic Athlete by Sheri Colberg and Edward Horton provides an in-depth explanation of this response as well as recommendations for adjusting insulin regimens and nutrient intake specific for various sports. You may also wish to contact the Diabetes, Exercise and Sports Association (DESA) which has a membership consisting of both recreational and competitive athletes with diabetes.