Managing glycemic fluctuations during exercise remains a key challenge for individuals with type 1 diabetes mellitus (T1DM), particularly when using continuous subcutaneous insulin infusion (CSII). A randomized crossover trial published in Diabetes Care compared glycemic responses and pharmacokinetics of ultra-rapid insulin lispro with standard insulin lispro during basal rate reductions (BRRs) before exercise in active adults with T1DM.

The double-blind, four-period trial included 25 participants who performed 60 minutes of moderate-intensity walking at 45-55% of maximal oxygen consumption (VO₂max), 4 hours after a standardized meal. Two BRR strategies were evaluated: a 50% reduction initiated 60 minutes before exercise and a 100% reduction initiated 15 minutes before exercise. The primary endpoint was the change in glucose during exercise, with pharmacokinetic outcomes assessed as secondary endpoints.

Ultra-rapid insulin lispro was associated with a smaller decline in glucose levels compared with standard insulin lispro during both BRR strategies (−26.8 ± 37 vs −39.0 ± 39 mg/dL and −46.9 ± 32 vs −60.5 ± 39 mg/dL). Circulating insulin levels increased early during exercise, but peak concentrations were lower with ultra-rapid insulin lispro. Fewer hypoglycemic events were observed with ultra-rapid insulin lispro. Following exercise, faster absorption was associated with earlier postprandial glucose reduction.

These findings indicate that ultra-rapid insulin lispro may support improved glycemic stability during exercise when used with CSII, although further studies may help confirm these observations in broader populations.