Unsupervised high-intensity interval training improves glycaemic control but not cardiovascular autonomic function in type 2 diabetes patients: A randomised controlled trial
Question
Does unsupervised HIIT improve glycaemic control and cardiovascular autonomic function in adults with type 2 diabetes compared with standard care?
Summary
Adults with type 2 diabetes were randomized to 12 weeks of mostly unsupervised gym-based cycling HIIT or standard care. The HIIT group completed all sessions and had better between-group HbA1c change than control, but cardiovascular autonomic measures such as heart-rate variability, blood-pressure variability, and baroreflex sensitivity did not improve meaningfully. The study was small, powered for HbA1c rather than autonomic function, and used a clinical type 2 diabetes population.
Methodology
- Adults with type 2 diabetes stable on diet and/or metformin, obese on average, randomized to HIIT or standard care.
- 22 participants.
- Cycle ergometer with light band-resisted upper-body exercise during recovery.
- Work intervals: 2 minutes in week 1, progressing by 10 seconds per week to 3 minutes 50 seconds in week 12.
- Recovery: 3 minutes after each interval: 90 seconds passive, 60 seconds light band exercise, 30 seconds preparation; 3-minute recovery cycle after final interval.
- Intensity: Pedal cadence >80 rpm and RPE 16-17 (very hard).
- Approximately 30 to 39 minutes based on reported structure.
- 3 sessions/week on non-consecutive days.
- 12 weeks.
- Randomized controlled trial comparing 12 weeks of HIIT with standard care.
- HbA1c, Heart rate variability, Blood pressure variability, and Baroreflex receptor sensitivity were tracked.
Outcomes
HbA1c
Between-group HbA1c change favored HIIT: intervention changed from 7.13 +/- 0.31% to 6.87 +/- 0.29%, while control changed from 7.18 +/- 0.17% to 7.36 +/- 0.21%.
Between-group P = 0.03.
Heart rate variability
No significant between-group changes in RRI, SDNN, LF/HF, or related HRV measures.
Examples from abstract: RRI P = 0.672; RRI LF/HF P = 0.203.
Blood pressure variability
Most BPV measures did not differ between groups, but systolic BP high-frequency normalized units worsened/decreased in the HIIT group.
SBP HFnu changed from 19 +/- 4 to 15 +/- 3 in HIIT and 28 +/- 5 to 28 +/- 3 in control; between-group P = 0.003. SBP LF/HF P = 0.169.
Baroreflex receptor sensitivity
HIIT did not significantly improve baroreflex receptor sensitivity compared with control.
Total slope mean between-group P = 0.150 in Table 3.
Baseline HbA1c and baroreflex sensitivity association
Higher HbA1c at baseline was associated with lower baroreflex receptor sensitivity.
rs = -0.592, P = 0.004.
Adherence
Analyzed intervention participants achieved maximal attendance and none dropped out.
36 +/- 0.9 sessions attended over 12 weeks.
Insights
- A structured mostly unsupervised cycle HIIT program can produce high adherence and improve HbA1c in carefully screened adults with type 2 diabetes.
- Short-term glycaemic improvement should not be translated into claims of improved cardiovascular autonomic regulation.
- Clinical HIIT programming needs explicit screening, contraindication, and medication boundaries.
Limitations
- Small sample size.
- Powered for HbA1c rather than autonomic function outcomes.
- Six randomized participants were lost during the study.
- Mostly male clinical sample.
- Intervention aimed to maintain weight, so findings do not test weight-loss-oriented HIIT.
- Control group changes in some autonomic measures were not fully explained.
Safety
- No adverse events or injuries were reported in the paper.
- Participants were screened by medical history, physical examination, ECG, and exercise stress testing.
- Overt cardiac disease, beta-blocker therapy, and exercise stress-test contraindications were exclusion criteria.