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
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.
Methodology
- Inactive adults with type 1 diabetes, BMI >=25 kg/m2, HbA1c 7.5-10.5%, and overweight or obesity.
- 30 participants.
- 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.
- Intensity: Heart-rate-guided: 85-95% HRpeak for high intervals.
- 33 min.
- 3 sessions per week.
- 12 weeks for primary intervention; some participants continued for 24 weeks.
- Randomized controlled trial with partial crossover of the control group to HIIT for a subsequent 12 weeks.
- HbA1c, CGM glycemic metrics, Blood pressure and arterial measures, and Body composition were tracked.
Outcomes
HbA1c primary comparison
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
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
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
There were no between-group differences in insulin dose or hypoglycemia on CGM.
Blood pressure, lipids, body weight, and body composition
No between-group differences were found for blood pressure, blood lipids, body weight, or body composition.
Exercise capacity and leg strength
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
One severe hypoglycemia event occurred immediately after supervised HIIT, with no adverse cardiac, respiratory, musculoskeletal, or ketoacidosis events reported.
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
- 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.