A cornerstone in the management and treatment of people living with type 1 diabetes (T1D) is to engage in regular physical exercise for a variety of health and fitness reasons. Despite these well-established benefits, many people with T1D experience their challenging glycaemic condition as a high barrier to exercise. The challenge of managing glycaemia around exercise together with fear of hypoglycaemia (FOH) remain major barriers to exercise in T1D patients, meaning that many are discouraged from exercise. If people with T1D wish to engage in exercise in a safe manner, a certain level of pre-planning before exercise is required in terms of insulin dosing and target glucose concentration.

Numerous research projects have been performed in the morning where participants exercise in the fasted state, for logistical reasons, because of easier insulin management in fasting conditions and a lower risk of hypoglycaemia during or after the exercise bout. However, in reality, advanced planning of exercise is not always possible, and many patients may also wish to exercise after their meal.

Hence, it is important to take into account the impact of prandial state on blood glucose responses to exercise in patients with T1D. While evidence on the importance of timing of exercise and on the benefits of postprandial exercise for improving glucose control is available in patients with type 2 diabetes, less studies have been conducted in T1D despite this being of high clinical importance.

Therefore, more insight is needed into the glycaemic and metabolic effects of different postprandial exercise modalities aiming to reduce the risk of hypoglycaemia and improve glucose control, both during and after exercise. Postprandial exercise can be a useful strategy to improve glycaemic control but research in T1DM is very scarce, with only few studies that have been conducted and optimal exercise regimens remaining unknown.

Summarizing, prandial state is an important factor to take into account in exercise in people with T1D, with glycaemic responses that substantially vary between fasted or postprandial exercise. Performing exercise in the postprandial period is of high clinical relevance however there is a scarcity of research in this area. Therefore, more studies that examine the glycaemic and metabolic effects of different modalities of postprandial exercise in people with T1D are needed. All of this aiming to simplify exercise-associated countermeasures and improve (postprandial) glucose control, and thereby reduce barriers to PA in this population.

Inclusion Criteria:

• Type 1 diabetes for ≥ 2 years and negative C-peptide (<100pmol/l)
• Male and female aged 18-65 years old
• HbA1c <9% (at least two values in a row in the past year), based on analysis from the central laboratory unit of Ghent University Hospital.
• Insulin treatment: multiple daily injections (MDI) or continuous subcutaneous insulin infusion (CSII): insulin pump alone without connection to sensor, or sensor-augmented pump (SAP) with or without stop at/before low; however no hybrid closed-loop systems will be included).
• Able to understand study instructions and to provide written informed consent.

Exclusion Criteria:

• Physical or psychological disease likely to interfere with the normal conduct of the study as judged by the investigator.
• Body mass index >= 35 kg/m2.
• Self-monitoring of blood glucose (SBMG) with finger prick
• CSII with a hybrid closed-loop insulin pump
• Taking any medication that affects heart rate.
• Current treatment with drugs known to interfere with metabolism, e.g. systemic corticosteroids, SGLT2 inhibitors, glucagon-like-peptide 1 (GLP-1) receptor agonists, or metformin.
• Hypoglycaemic unawareness (Gold score ≥4) or having experienced any episode of a severe hypoglycaemic event within the last 6 months (i.e. need of third-party assistance).
• Known coronary or cerebral artery disease, i.e. history of angina pectoris, myocardial infarction (MI), stroke or any cardiovascular procedure.
• Severe non-proliferative and unstable proliferative retinopathy, based on medical record.
• Severe diabetic peripheral neuropathy (DPN) or autonomic neuropathy, based on medical record.
• Uncontrolled hypertension (>180/100 mmHg).
• Pregnant or planning to become pregnant during the study period (females)
• Breastfeeding (females).