Despite the promising data emanating from trials investigating the effectiveness of advanced hybrid closed loop (AHCL) insulin delivery systems in managing glycaemia in those with type 1 diabetes (T1D), we currently know little about their efficacy in optimising glycaemia when physical activity is factored into the equation. With the introduction of new AHCL systems that have novel technological features, we are left with important questions of how to optimise their use around physical exercise to not only minimise dysglycaemia, but also encourage individuals with T1D to lead a physically active lifestyle for the associated wider health benefits.

This will be a three-period, randomised, cross-over study with a single-hormone (insulin) AHCL system that compares the efficacy of three insulin management strategies: (i) unannounced exercise and a full dose of meal-time insulin 90-minutes prior to commencement, (ii) a 25% reduced dose of meal-time insulin with exercise announcement 90-minutes prior to commencement and (iii) a 25% dose reduction in meal-time insulin with exercise announcement 45-minutes prior to commencement, in optimising TIR around dynamic physical exercise in adults with T1D.

Following successful completion of a screening visit, participants will attend the laboratory to complete 3 experimental visits during which they will undertake a 45-minute bout of moderate intensity continuous exercise on a bicycle ergometer at ~60% VȮ2max. Prior to commencing exercise, participants will consume a standardised low-glycaemic index, carbohydrate-based meal (equating to 0.75g.CHO.kg.bm-1) with, or without, a 25% reduction in their meal-time insulin dose as well as with, or without exercise announcement (according to the randomisation). Exercise announcement will increase the individualised target glucose levels to 8.3 mmol.L-1. Venous blood glucose sampling will be taken in 15-minute intervals leading into and after exercise with 5-minute intervals performed during exercise. Samples will be used to retrospectively cross-compare trial day glycaemic responses between visits. Each participant will undertake 1 screening and 3 experimental visits equating to a total of 80 study visits

Inclusion Criteria:

• • Type 1 diabetes ≥2 years.

  • HbA1c;

    • 58-63 mmol/mol (maximum 30% of participants) OR
    • ≥ 64 mmol/mol (minimum 70% of participants)

  • Insulin pump treatment ≥12 months

  • CGM or isCGM use ≥6 months

  • Novorapid use ≥4 weeks

  • Carbohydrate counting and use of the insulin pump bolus calculator for most snacks and meals.

  • Carbohydrate intake >80 grams per day (assessed by review of intake recorded in the insulin pump during the 2 weeks prior to the screening visit)

Exclusion Criteria:

• • Breast-feeding, pregnancy or planning to become pregnant.

  • Use of anti-diabetic medicine (other than insulin), corticosteroids or other drugs affecting glucose metabolism during the study period or within 30 days prior to study start.
  • Use of hybrid closed-loop systems
  • Daily use of paracetamol (acetaminophen)
  • Alcohol or drug abuse.
  • Severe cardiac disease or retinopathy contraindicating HbA1c <53 mmol/mol.
  • Other concomitant medical or psychological condition that according to the investigator's assessment makes the person unsuitable for study participation.
  • Lack of compliance with key study procedures at the discretion of the investigator.
  • Unacceptable adverse events at the discretion of the investigator.