Insulin pumps are gaining in popularity for insulin delivery but there is no consensus regarding guidelines for proper pump use during exercise, Dr. Admon and colleagues point out in their report.

They determined the cardiorespiratory, metabolic, and hormonal responses to controlled submaximal exercise with the insulin pump on (at 50% of the basal rate) and the pump off in 10 type 1 diabetic patients 10 to 19 years of age.

The subjects exercised for 40 to 45 minutes on a cycle ergometer roughly 2 hours after a standard breakfast and an insulin (Lispro) bolus. They consumed 20 grams of carbohydrates before and after exercising. Each subject exercised once with the pump on and once with the pump off in a randomized, crossover fashion.

"Children engage frequently in unplanned physical activity (and) our study was designed to mimic unplanned exercise," the authors note.

This type of exercise, the researchers found, "is equally performed, perceived, and safe (in terms of acute hypoglycemia)" with the pump on or with the pump off.

During exercise, blood glucose levels fell by 59 mg/dL with the pump off and by 74 mg/dL with the pump on. These differences were not significant. There were also no significant differences in cortisol, growth hormone, or noradrenaline levels between pump modes or in cardiorespiratory parameters, blood lactate levels or free fatty acid concentrations.

The team did find that late hypoglycemia was more common than acute hypoglycemia (during exercise) and there was a trend toward increased risk of late hypoglycemia with the pump on during exercise. Nine subjects had late hypoglycemia after on-pump exercise compared with six after off-pump exercise.