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751-P: Effect of Morning (Fasting) vs. Afternoon High-Intensity Interval Exercise on Blood Glucose in Type 1 Diabetes

Studies of high intensity interval training (HIIE) in individuals with type 1 diabetes (T1D) have had variable blood glucose outcomes, including increases, decreases, and no significant change during and after exercise. A potential unaccounted factor that may influence these outcomes is the time of day during which participants exercise. We hypothesized that morning (fasting) exercise (AMx) would increase blood glucose levels, while afternoon exercise (PMx) would decrease blood glucose levels throughout exercise (45 min) and recovery (60 min). Ten individuals with T1D (4M/6F) aged 31±6.6 years, with VO2peak 42.2±7.2 mLO2·kg-1·min-1, and diabetes duration 18.7±10.3 years, performed a HIIT protocol both while fasting in the morning (7 am), and in the late afternoon (5 pm). Sessions were separated by at least 48 hours, with the order randomly assigned. A standard snack was provided one hour prior to PMx to replicate previous study designs. The HIIE protocol consisted of a warm-up (10 min), 12 maximal sprints (10 seconds every 2 minutes - 24 min), and a cool down (11 min). Exercise was followed by a monitored recovery period (60 min). Capillary glucose (CG) was recorded at baseline, at the end of exercise, and 60 minutes post-exercise. Data were analyzed using a 2X3 ANOVA. An interaction of time and condition (p = 0.017) was found, indicating that CG levels followed different trajectories during AMx and PMx. Changes in CG during exercise were not significantly different between conditions (AMx = +1.8±2.6 vs. PMx = -0.4±3.2 mmol/L; p=-.141). Changes during the 60-minute recovery were significantly different (p=0.039) with the AMx condition resulting in a continued increase in CG (+0.4±1.5 mmol/L) while CG declined during recovery in PMx (-1.2±2.8 mmol/L). The design of future studies of HIIE in T1D, as well as recommendations for insulin adjustments and carbohydrate intake, should take into account the time of day that exercise is performed. Disclosure J.E. Yardley: Research Support; Self; Abbott, Dexcom, Inc., LifeScan Canada. Speaker9s Bureau; Self; Dexcom, Inc. Funding Augustana College