Inclusion Criteria:  T1D diagnosis more than 6 months ago Using a basal bolus insulin regime or insulin pump therapy BMI ≤ 32 kg.m-2  Exclusion Criteria:  Pregnancy (or planning pregnancy) Disability preventing participation in an exercise regime Angina Autonomic neuropathy Medication that affects heart rate (this will affect estimation of fitness) Major surgery planned within 6 weeks of study Uncontrolled blood pressure Significant history of hyperglycaemia History of severe hypoglycaemia requiring third party assistance within the last 3 months Severe non-proliferative and unstable proliferative retinopathy