Staying Safe During (and After) Vigorous Exercise

Q: My husband has type 1 diabetes and is training to ride in a 65-mile bicycle race. How can he best control his blood sugar levels during and after this race? His levels sometimes crash a few hours after training.

A:First, I would like to congratulate your husband on having the remarkable discipline such an activity requires. This is long and strenuous exercise. I am assuming that he has been evaluated and cleared by his doctor to participate in such physical activity, so I will focus on glucose control. When engaging in arduous exercise, people who have diabetes should be vigilant about preventing both high and low glucose levels.

The risk of low sugar levels is more intuitive to understand than high sugar levels because the body uses so much energy from glucose during exercise. In addition, after exercising, the body tries to replenish the energy stores of the muscles and the liver, which can also lead to abnormally low blood sugar levels.

High sugar levels can develop because the body considers long and strenuous exercise a form of stress. Any type of stress triggers the production of adrenaline and other hormones that inhibit insulin and increase the production of glucose. Here are some general guidelines.

Before training begins, your husband should have his diabetes controlled very well with intense insulin therapy, either with three or more injections a day or with an insulin pump. This allows for better flexibility during his training and race.
During his training weeks or months, your husband should monitor his glucose levels both before and after meals. He should also track the amount of insulin he injects, his dietary intake, and the duration of each exercise or training session. He should also check his glucose levels at 2 a.m.

Before he starts his training sessions, he should determine his glucose level. The ideal glucose level is 100 to 250 mg/dl. If it is below 100 mg/dl, then he must eat a snack containing carbohydrates. If it's above 250 mg/dl, he should also check for the presence of ketones in his urine. Ketones are the by-product of fat energy metabolism. The body reverts to this process when it lacks sufficient amounts of insulin. If he has urine ketones, he should refrain from exercising until the insulin deficiency is corrected. If his sugar is above 300 mg/dl, he must postpone his training session until his levels are corrected.

While he's training, your husband should check his glucose level frequently. He should also carry drinks that contain carbohydrates, or sugar tablets, to compensate for low levels. Having a "map" of his sugar levels (see step 2) will provide him a reference to base his insulin requirement on as well.

After exercising, your husband's body will try to restore the glucose in his muscles and liver, so it will continue to remove glucose from the bloodstream. This leads to low sugar levels even hours after he's through exercising. Your husband must check his glucose level immediately after exercising and several times later, for up to 12 hours afterwards.

Based on the records he has kept on his glucose levels, he may need to reduce his insulin dose by more than 50 percent.

It is best to exercise at least 30 minutes after injecting insulin to limit the effect of exercise on insulin absorption. If your husband exercises in the afternoon or evening, he might find his glucose level to be abnormally low in the middle of the night — his bedtime or evening insulin doses would have to be adjusted accordingly. If your husband is on NPH, the evening dose should be given at 10 or 11 p.m. Your husband will probably need to increase his carbohydrate intake in the evening to prevent low blood sugar levels in the middle of the night.

It is also generally recommended that diabetic athletes have a meal two to six hours before exercising. It should contain 83 to 200 grams of carbohydrate, a small amount of protein, and fat.