Challenges Associated With Exercise Studies in Type 1 Diabetes

Abstract

In type 1 diabetes (T1D), even short bursts of physical activity can affect blood glucose.1,2 Fear of hypoglycemia is a barrier to exercise participation, and prevention of early and overnight hypoglycemia following activities is a major concern.3 In our development of closed-loop artificial pancreas systems, we have observed that physical activity can lead to hypoglycemia despite suspension of insulin delivery.4 Thus, to inform and improve upon these systems, 5 we compared changes in glycemia following 2 sprinting bouts of differing durations.After signing informed consent, 12 recreationally active, healthy adults (7 F, 5 M) with T1D (42.2 ± 15.4 years, mean ± SD) participated. On day 1, subjects were fitted with a Dexcom G4®Platinum CGM (Dexcom®, San Diego, CA), an ActiGraph wGT3X-BT activity monitor (ActiGraph, Pensacola, FL), and a Polar® heart rate monitor (Polar Electro Oy, Finland). On Days 2 and 4, subjects consumed a Glucerna® Hunger Smart™ Shake containing 14-16 grams carbohydrate for breakfast, for which they took a usual dose of rapid-acting insulin. Three hours later, when insulin and glucose levels were stable, they performed a supervised 10-or 60-second sprint in randomized order at a local track.While heart rate and energy expenditure differed between sprints trials (P < .001), no differences were noted between presprint and postsprint fingerstick blood glucose levels. However, their CGM glucose values during 30 minutes post 10-second sprints had a greater percentage of time in the 80-140 mg/dL range (median 92.9% [IQR 0-100]) than following the 60-second sprints (0% [0-21.4], P < .05). This finding was primarily the result of a higher starting glucose level before exercise, as neither the 10-second nor 60-second sprint caused a clinically significant change in median glucose levels over the 30-minute period: -7.5 mg/dL [-16, -5] (P = ns) for the 10-second sprint versus +28.5 mg/dL [-2, +34] (P = ns) for the 60-second sprint (Figure 1). In addition, 5 subjects (42%) consumed carbohydrates either just before or within the hour after the sprints. There were no differences in time spent <70 mg/dL or in the number of hypoglycemic events during the 30 minutes postsprints and no differences in any 625084D STXXX10.1177/1932296815625084Journal