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Diabetes Technol Ther. 2016 Dec;18(12):794-799.

Mitigating Reductions in Glucose During Exercise on Closed-Loop Insulin Delivery: The Ex-Snacks Study.

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Yale School of Medicine , Yale Pediatric Endocrinology & Diabetes, New Haven, Connecticut.



To assess whether snacking could be used with closed-loop (CL) insulin delivery to avoid exercise-induced reductions in plasma glucose (PG), as well as elevations in PG at the end of exercise.


Twelve type 1 diabetes (T1D) subjects (age 13-36 years, duration 10.7 ± 8.4 years, A1c 7.4% ± 0.8% [57 ± 8.7 mmol/mol]) underwent two 105-min exercise studies while under CL control: CL alone and CL+snack. Exercise, commenced at 3 PM, consisted of four 15-min periods of brisk treadmill walking to 65%-70% HRmax (separated by three 5-min rest periods), followed by a 30-min recovery period. Fifteen to 30 g carbohydrate (Gatorade) was provided on snacking visits just before and midway through the exercise period. PG and insulin were measured every 15-20 min during the exercise studies.


Baseline PG levels were similar for CL alone (164 ± 16 mg/dL) versus CL+snack (172 ± 11 mg/dL). During exercise, PG levels fell by 53 ± 10 mg/dL without snacking versus a modest 10 ± 13 mg/dL increase in PG with snacking (P = 0.0005); similar differences in the change in PG levels were observed at the end of recovery period. Hypoglycemia requiring rescue treatment (PG ≤60 mg/dL) during exercise occurred in three nonsnacking visits versus none with snacking. During the 75-min exercise period, insulin delivered was 1.8 ± 0.4 U for the CL+snack admission compared to 0.7 ± 0.1 U during CL alone (P = 0.002).


These results support the use of a simple snacking strategy to avoid exercise-induced lowering of PG while on CL insulin delivery. Persistent insulin infusion during exercise with snacking also appears to be effective in limiting increases in PG at the end of exercise.


Artificial pancreas; Carbohydrate counting; Closed-loop systems; Pediatrics; Type 1 diabetes

[Indexed for MEDLINE]
Free PMC Article

Conflict of interest statement

Author Disclosure Statement Medtronic Diabetes provided the pumps, sensors, infusion sets, reservoirs, and Android phones for the CL experiments. W.V.T. is a consultant for Medtronic Diabetes, NovoNordisk, and Sanofi. S.A.W. is a consultant for Medtronic Diabetes and Tandem, and serves on a Medical Advisory Board for Insulet. E.C. is a speaker for NovoNordisk. No other potential conflicts of interest relevant to this article were reported. No sponsor had any role in the study design, data collection, data analysis, data interpretation, or writing of the report.

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