Glycaemia Around Exercise in People With Type 1 Diabetes With and Without a Bolus Calculator: A Post Hoc Analysis of a Randomised Controlled Trial

INTRODUCTION: Exercise-induced hypoglycaemia is a barrier to physical activity in people with type 1 diabetes. Clinical guidelines recommend reducing prandial insulin before aerobic exercise, but adherence is limited. Insulin bolus calculators may support implementation of these recommendations, yet their effect on glucose around exercise is not well described.

METHODS: This post-hoc analysis used data from a randomised crossover trial including 17 adults with type 1 diabetes treated with multiple daily injections. Participants completed 45 minutes of moderate-intensity cycling after breakfast using either the Hedia Diabetes Assistant (HDA) bolus calculator smartphone app (50% bolus reduction) or their habitual diabetes management. Continuous glucose monitoring data were analysed from an hour before to an hour after exercise. Linear mixed-effects models were used to estimate the glucose rate of change.

RESULTS: In all participants, glucose increased before exercise (0.040 mmol/L/min [95% confidence interval [CI] = 0.030, 0.050]), declined during exercise (-0.039 mmol/L/min [95% CI = -0.058, -0.020]), and plateaued post-exercise (0.002 mmol/L/min [95% CI = -0.025, 0.030]). Pre-exercise, the increase in glucose was higher when using HDA (mean difference = 0.043 mmol/L/min [0.023, 0.062]), lower during exercise (mean difference = 0.030 mmol/L/min [95% CI = -0.003, 0.063]), and similar post-exercise (mean difference = 0.002 mmol/L/min [95% CI = -0.025, 0.030]). Two hypoglycaemic events occurred during control sessions and none during HDA sessions.

DISCUSSION: The use of an insulin bolus calculator implementing insulin reduction appeared to reduce the glucose decline during aerobic exercise, potentially reducing hypoglycaemia risk. However, increases in pre-exercise glucose indicate that a 50% reduction for moderate-intensity exercise may be excessive for some.