Abstract 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 2peak . 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 −1 ) and all other conditions (all p > 0.05), yet fell more in the 50% IAsp dose (−5.1 ± 3.0 mmol L −1 ) compared to the URA‐IAsp (−2.8 ± 3.3 mmol L −1 ) and IAsp (−3.4 ± 3.3 mmol L −1 ) 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.
Pitt et al. (2026) studied this question.