# Unsupervised high-intensity interval training improves glycaemic control but not cardiovascular autonomic function in type 2 diabetes patients: A randomised controlled trial PMID: 30541346 Journal: Diabetes & Vascular Disease Research Published: 2019-01 Authors: Cassidy S, Vaidya V, Houghton D, Zalewski P, Seferovic JP, Hallsworth K, MacGowan GA, Trenell MI, Jakovljevic DG ## 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. ## Population - Adults with type 2 diabetes stable on diet and/or metformin, obese on average, randomized to HIIT or standard care. - Sample size: 22 - Age: Approximately 60 years; control 59 +/- 3 and intervention 60 +/- 3 years. - Sex: 17 males and 5 females in final analyzed groups. - Fitness level: Low-active; excluded if >=60 min moderate-vigorous activity per week. - Health status: Type 2 diabetes; average BMI about 31-32 kg/m2; no overt cardiac disease by screening. ## Methodology - Randomized controlled trial comparing 12 weeks of HIIT with standard care. - 12 weeks - Clinical Research Facility, Royal Victoria Infirmary, Newcastle upon Tyne for testing; local gym for HIIT sessions. - Randomized and controlled study design. ## Protocol - Mostly unsupervised cycle HIIT. - Modality: 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. - Sets or repetitions: Five intervals. - Intensity: Pedal cadence >80 rpm and RPE 16-17 (very hard). - Session duration: Approximately 30 to 39 minutes based on reported structure. - Frequency: 3 sessions/week on non-consecutive days. - Program length: 12 weeks. - Progression: Work interval duration increased by 10 seconds each week. - Standard care control. - Program length: 12 weeks. - Progression: Asked to maintain normal routine and not change medication, physical activity, diet, or body weight. ## Outcomes ### HbA1c Status: improved 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 Status: no clear change 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 Status: mixed 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 Status: no clear change 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 Status: mixed Higher HbA1c at baseline was associated with lower baroreflex receptor sensitivity. rs = -0.592, P = 0.004. ### Adherence Status: improved Analyzed intervention participants achieved maximal attendance and none dropped out. 36 +/- 0.9 sessions attended over 12 weeks. ## Practical 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 And Adherence - No adverse events or injuries were reported in the extracted full text. - 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. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/30541346/) (pubmed) - [DOI](https://doi.org/10.1177/1479164118816223) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6327303/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.