I am a 20 year old international competitive swimmer who has had type�1 diabetes for about six years. Can you advise me on the effects of varying my blood sugar on my performance? Will my performance be better or worse with a high/low blood sugar?

For optimal performance, you will want your blood sugar to be as close to normal range as possible, without risking a low blood sugar. For many people on insulin, that is most easily accomplished by starting exercise with a blood sugar in the range of 150-180 mg/dl [8.3-10 mmol/L]. Insulin pump users may be able to exercise with near normal blood glucose levels without risking hypoglycemia by decreasing or suspending insulin basal rates. You don’t specify your insulin regimen or the distance you swim, but you should take these into consideration as they will effect the direction and degree of change in blood sugar related to exercise.

Generally, short duration, “explosive type” exercise (sprinting distances) will not significantly decrease blood sugar, and may actually cause a rise in blood sugar. This rise is related to hormonal influences and liver glycogen output. Beginning exercise with a high blood sugar may cause you to feel fatigued and perform poorly. As carbohydrate (glucose) is the essential fuel for energy production, you will also find the intense muscle contraction of competitive exercise nearly impossible with a low blood sugar as well. Again, your best performance will come with optimal blood glucose control – both during training and competition. Work with your diabetes team to find a management regimen that works for you.

DMW

[Editor’s comment: Gary Hall Jr. won two gold medals and two silver medals at the 1996 Olympic Games in Atlanta, and recently added to that total, winning two golds, one silver and one bronze at the 2000 Olympic Games in Sydney. See: Gary Hall Jr. Olympic Diary and Back from the Edge.

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