# Effect of High-Intensity Interval Training on Glycemic Control in Adults With Type 1 Diabetes and Overweight or Obesity: A Randomized Controlled Trial With Partial Crossover PMID: 32647051 Journal: Diabetes Care Published: 2020-09 Authors: Lee AS, Johnson NA, McGill MJ, Overland J, Luo C, Baker CJ, Martinez-Huenchullan S, Wong J, Flack JR, Twigg SM ## Question Can 12 weeks of high-intensity interval training reduce HbA1c and improve cardiometabolic risk factors in inactive adults with type 1 diabetes and overweight or obesity? ## Summary Thirty inactive adults with type 1 diabetes and overweight or obesity were randomized to 12 weeks of HIIT or usual care, with the control group later crossing over to HIIT. The primary 12-week comparison did not show a statistically significant HbA1c reduction versus control, although participants who completed at least half of prescribed sessions had a greater HbA1c reduction. The program used 33 min sessions, three times weekly, with 4 x 4 min intervals at 85-95% peak heart rate. One severe hypoglycemia event occurred immediately after a supervised HIIT session in the first week, while no adverse cardiac, respiratory, musculoskeletal, or ketoacidosis events were reported. ## Population - Inactive adults with type 1 diabetes, BMI >=25 kg/m2, HbA1c 7.5-10.5%, and overweight or obesity. - Sample size: 30 - Age: 44 +/- 10 years overall in abstract; randomized groups 40.5 +/- 10.0 and 46.1 +/- 10.5 years. - Sex: 16 male and 11 female among 27 participants with 12-week outcome data; randomized baseline table shows HIIT 6 male/6 female and control 10 male/5 female. - Fitness level: Inactive; less than 150 min/week moderate exercise for previous 6 months. - Health status: Type 1 diabetes for >1 year with overweight or obesity and HbA1c above target. ## Methodology - Randomized controlled trial with partial crossover of the control group to HIIT for a subsequent 12 weeks. - 12-week randomized comparison, with 24-week follow-up/partial crossover structure. - Charles Perkins Centre, University of Sydney, with at least one supervised gym session per week and additional home or own-gym sessions. - Randomized and controlled study design. ## Protocol - HIIT. - Modality: Cycle ergometer or treadmill in facility; walking or jogging at home. - Work intervals: 4 min at 85-95% HRpeak. - Recovery: 3 min at 50-70% HRpeak. - Sets or repetitions: 4 high-intensity bouts with 3 recovery bouts. - Intensity: Heart-rate-guided: 85-95% HRpeak for high intervals. - Session duration: 33 min. - Frequency: 3 sessions per week. - Program length: 12 weeks for primary intervention; some participants continued for 24 weeks. - Progression: No explicit progression in interval dose; continued protocol with transition to unsupervised sessions in study period 2 for original intervention group. - Usual care control. - Modality: Usual daily activities. - Program length: 12 weeks before partial crossover. - Progression: No structured exercise recommendation or restriction. ## Outcomes ### HbA1c primary comparison Status: no clear change HbA1c decreased within the HIIT group, but the between-group change versus control did not reach statistical significance. HIIT -0.53 +/- 0.61% versus control -0.14 +/- 0.48%, p = 0.08; within HIIT baseline 8.63 +/- 0.66% to 8.10 +/- 1.04%, p = 0.01. ### HbA1c among adherent participants Status: improved Participants who completed at least 50% of prescribed HIIT had a significantly greater HbA1c reduction than control. HIIT -0.64 +/- 0.64% (n = 9) versus control -0.14 +/- 0.48% (n = 15), p = 0.04. ### Longitudinal HbA1c after completing HIIT Status: improved Across 24 participants who completed a 12-week HIIT intervention, HbA1c decreased significantly. -0.40 +/- 0.62%, p = 0.006. ### Insulin dose and CGM hypoglycemia Status: no clear change There were no between-group differences in insulin dose or hypoglycemia on CGM. ### Blood pressure, lipids, body weight, and body composition Status: no clear change No between-group differences were found for blood pressure, blood lipids, body weight, or body composition. ### Exercise capacity and leg strength Status: improved The intervention group improved maximal treadmill exercise test time and leg press strength, without a significant VO2peak change. Bruce protocol time p = 0.001 within HIIT; leg press p < 0.001 within HIIT. ### Safety Status: mixed One severe hypoglycemia event occurred immediately after supervised HIIT, with no adverse cardiac, respiratory, musculoskeletal, or ketoacidosis events reported. ## Practical Insights - The 4 x 4 min aerobic HIIT structure is reproducible but depends on heart-rate monitoring and adherence. - For type 1 diabetes, HIIT programming needs explicit hypoglycemia planning and individualized insulin/carbohydrate support. - Modest adherence may be enough for a glycemic signal, but average adherence was only about two sessions per week despite support. - HIIT should not be framed as clearly improving HbA1c in this population based on the primary randomized comparison alone. ## Limitations - Primary HbA1c comparison did not reach statistical significance. - Small sample and modified intention-to-treat based on participants with 12-week outcome data. - Suboptimal exercise adherence. - Control-group physical activity was not restricted or explicitly measured. - No active exercise comparator. - Diabetes consultation intensity differed between intervention and control conditions. - Dietary changes were not quantified. - VO2peak measurement reliability may have been affected by mask leakage and gas analyzer service repair. - Clinical population limits generalization to general fitness users. ## Safety And Adherence - One severe hypoglycemia event occurred immediately after a supervised HIIT session in the first week. - The participant could not drink juice because of nausea and was treated with parenteral glucose plus short emergency department observation. - There was no loss of consciousness. - Contributing factors included mild hypoglycemia earlier that day and difficulty managing glucose when initiating a new exercise program. - No adverse cardiac events, respiratory events, musculoskeletal injuries related to HIIT, or diabetic ketoacidosis were reported. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/32647051/) (pubmed) - [DOI](https://doi.org/10.2337/dc20-0342) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7440893/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.