High-intensity interval training and hypoglycaemia minimisation in adults with type 1 diabetes

INTERVENTION: Study participants will have initial baseline cardiorespiratory fitness testing on a cycle ergometer and an exercise protocol familiarisation session in the Charles Perkins Centre (CPC) gym. Participants will wear a FreeStyle Libre Pro flash glucose monitor for the entire duration of the study. The glucose recordings on the FreeStyle Libre Pro flash glucose monitor remain masked to the participant for the entire duration of the study. The FreeStyle Libre Pro flash glucose monitor data is subsequently downloaded and used in analysis. Participants will be advised to continue routine fingerprick glucose testing, such as premeals, post‐meals and at bedtime. They will have a baseline overnight continuous glucose recording with FreeStyle Libre Pro flash glucose monitor (with no exercise in the preceding 2 days) on their usual insulin regimen. Participants will undertake a total of 4 exercise intervention sessions within 4 weeks of wearing a flash glucose monitor, with at least 2 days between exercise sessions. All exercise sessions will be supervised by a study investigator, thus ensuring adherence to the intervention and achievement of target exercise intensity. Participants will be randomised to complete either the HIIT series (3 sessions) or continuous exercise (1 session) first in a cross‐over design. Participants will be asked to avoid caffeine, alcohol and exercise for 24hours prior to each exercise intervention session. Participants will follow their usual home diet and insulin routine on the day of each exercise intervention session, and will arrive at the Charles Perkins Centre Gym at 4pm (at least 2 hours after lunch with usual insulin bolus) to commence the supervised exercise session. They will then go home and have dinner with 75% of their usual insulin:carb bolus and 75% of their usual correction insulin dose if needed. Participants will be asked to have a similar dinner on all exercise days. At 9pm on intervention exercise nights, all participants will consume a 15gram carbohydrate‐containing snack (with 75% of their usual insulin bolus and 75% of their usual correction if they would usually bolus for snacks) before bed, and instructed to ensure blood glucose is>7.0 mmol/L before bed, with consumption of extra carbohydrate intake to achieve this if required. HIIT exercise intervention session: High intensity interval training (HIIT) exercise will consist of 33minutes of supervised exercise on a cycle ergometer: After 5minutes of warm‐up at approximately 60% peak heart rate, participants will do 4 bouts of 4‐minute high‐intensity intervals at 85‐95% peak heart rate interspersed with 3 bouts of 3‐minute recovery intervals at 50‐70% peak heart rate. The exercise session will conclude with 3minutes of cool‐down at approximately 50% peak heart rate. That night, the participant will administer basal insulin at 10% reduction, 20% reduction or 30% reduction of their usual dose (HIIT10, HIIT20, HIIT30 intervention sessions respectively). CONDITION: Type 1 diabetes PRIMARY OUTCOME: Total duration (minutes) of overnight hypoglycaemia following afternoon HIIT exercise with varying basal insulin‐dose reductions of 10%, 20% and 30% (HIIT10, HIIT20, HIIT30) compared to continuous moderate‐intensity aerobic exercise with basal insulin‐dose reduction of 20% (Cont20) and non‐exercise baseline with no basal insulin‐dose reduction. This will be measured using data from the Freestyle Libre Pro Flash glucose monitor. SECONDARY OUTCOME: % glucose in hyperglycaemic range. ; This will be measured using data from the Freestyle Libre Pro Flash glucose monitor. % glucose in hypoglycaemic range. ; This will be measured using data from the Freestyle Libre Pro Flash glucose monitor. % glucose in target range 4.0‐10.0mmol/L. ; This will be measured using data from the Freestyle Libre Pro Flash glucose monitor. ; Aortic diastolic pressure (mmHg). This will be measured using non‐invasive applanation tonometry (SphygmoCor XCEL PWA and PWV System). Aortic mean arterial pressure (mmHg). This will be measured using non‐invasive applanation tonometry (SphygmoCor XCEL PWA and PWV System). Aortic pulse pressure (mmHg). This will be measured using non‐invasive applanation tonometry (SphygmoCor XCEL PWA and PWV System). Aortic systolic pressure (mmHg). This will be measured using non‐invasive applanation tonometry (SphygmoCor XCEL PWA and PWV System). Area under the curve for glucose less than or equal to 3.9mmol/L. ; This will be measured using data from the Freestyle Libre Pro Flash glucose monitor. Augmentation index (%). This will be measured using non‐invasive applanation tonometry (SphygmoCor XCEL PWA and PWV System). Augmentation index calculated for a heart rate of 75 beats per minute (%). This will be measured using non‐invasive applanation tonometry (SphygmoCor XCEL PWA and PWV System). Diastolic blood pressure (mmHg). This will be measured using a sphygmomanometer on the upper arm. Glucose nadir (mmol/L). ; This will be measured using data from the Freestyle Libre Pro Flash glucose monitor. Glucose peak (mmol/L) ; This will be measured using data from the Freestyle Libre Pro Flash glucose monitor. Glucose variability ‐ coefficient of variation. ; This will be measured using data from the Freestyle Libre Pro Flash glucose monitor. Glucose variability ‐ interquartile range. ; This will be measured using data from the Freestyle Libre Pro Flash glucose monitor. Glucose variability ‐ Standard deviation. ; This will be measured using data from the Freestyle Libre Pro Flash glucose monitor. Mean duration of hyperglycaemic episodes (minutes). ; This will be measured using data from the Freestyle Libre Pro Flash glucose monitor. Mean duration of hypoglycaemic episodes (minutes). ; This will be measured using data from the Freestyle Libre Pro Flash glucose monitor. Number of episodes of hyperglycaemia/night. ; This will be measured using data from the Freestyle Libre Pro Flash glucose monitor. Number of episodes of hypoglycaemia/night. ; This will be measured using data from the Freestyle Libre Pro Flash glucose monitor. Overnight mean glucose (mmol/L) ; This will be measured using data from the Freestyle Libre Pro Flash glucose monitor. Pulse transit time (seconds). This will be measured using non‐invasive applanation tonometry (SphygmoCor XCEL PWA and PWV System). Pulse wave velocity (m/s). This will be measured using non‐invasive applanation tonometry (SphygmoCor XCEL PWA and PWV System). Systolic blood pressure (mmHg). This will be measured using a sphygmomanometer on the upper arm. INCLUSION CRITERIA: Age 18‐70 years,T1D > 1 year duration, HbA1c 6.5‐10.0%, Self‐manage diabetes with multiple‐daily insulin injections including a daily nocte dose of basal insulin or twice‐daily basal insulin, or subcutaneous insulin pump.