Insulin dose reduction during exercise yields similar glucose effects with ultra-rapid and rapid aspartWhen exercising with type 1 diabetes, does the type of fast-acting insulin matter?

AIMS: To compare the effects of dose reductions of ultra-rapid-acting insulin aspart (URA-IAsp) and rapid-acting insulin aspart (IAsp) on blood glucose concentrations during continuous moderate-intensity exercise in people with type 1 diabetes (T1D). MATERIALS AND METHODS: In this double-blind, laboratory-controlled study, 43 adults with T1D completed four experimental visits in a randomised crossover design. Participants injected a 50% or 75% reduced dose of URA-IAsp or IAsp with a standardised breakfast 60 min prior to 45 min of cycling at ~61% V̇O. The same insulin type and dose were administered 4 h after the first injection, alongside an identical lunch meal. Venous blood samples were taken at 5-, 10-, and 15-min epochs, for a total of 70 timepoints, throughout the trial day until 4 h after the second injection to determine blood glucose and insulin concentrations. The primary endpoint was the four-way comparison of blood glucose change from exercise start to end. RESULTS: Blood glucose declined during exercise to a similar extent between 50% dose URA-IAsp (-4.0 ± 2.8 mmol L) and all other conditions (all p > 0.05), yet fell more in the 50% IAsp dose (-5.1 ± 3.0 mmol L) compared to the URA-IAsp (-2.8 ± 3.3 mmol L) and IAsp (-3.4 ± 3.3 mmol L) 75% reduced dose conditions (both p < 0.05). Differences in blood insulin concentrations between trials were only resultant of insulin doses and not insulin type from 30 min after the first insulin injection. CONCLUSIONS: Insulin dose reductions around acute moderate-intensity exercise yield similar glucose-lowering effects with URA-IAsp and IAsp. The extent of dose reductions exerts greater influence on glycaemia than the type of fast-acting insulin.