Unsupervised high-intensity interval training improves glycaemic control but not cardiovascular autonomic function in type 2 diabetes patients: A randomised controlled trial

Background: This is the first randomised controlled trial to assess the impact of unsupervised high-intensity interval training on cardiovascular autonomic function in adults with type 2 diabetes. Methods: A total of 22 individuals with type 2 diabetes (age 60 +/- 2 years, 17 males) lay in a supine position for 20 min for evaluation of cardiovascular autonomic function, which included (1) time domain measures of heart rate variability, (2) frequency domain measures of heart rate variability and blood pressure variability and (3) baroreflex receptor sensitivity. Participants were randomised into 12 weeks of high-intensity interval training (3 sessions/week) or standard care control group. Results: After 12 weeks, the between-group change in HbA(1c) (%) was significant (high-intensity interval training: 7.13 +/- 0.31 to 6.87 +/- 0.29 vs Control: 7.18 +/- 0.17 to 7.36 +/- 0.21, p = 0.03). There were no significant changes in measures of heart rate variability; R-R interval (ms) (high-intensity interval training: 954 +/- 49 to 973 +/- 53 vs Control: 920 +/- 6 to 930 +/- 32, p = 0.672), low frequency/high frequency (high-intensity interval training: 0.90 +/- 0.21 to 0.73 +/- 0.07 vs Control: 1.20 +/- 0.29 to 1.00 +/- 0.17, p = 0.203), or blood pressure variability; systolic blood pressure low frequency/high frequency (high-intensity interval training: 0.86 +/- 0.21 to 0.73 +/- 0.10 vs Control: 1.06 +/- 0.26 to 0.91 +/- 0.14, p = 0.169). At baseline, HbA(1c) was negatively correlated with baroreflex receptor sensitivity (r = -0.592, p < 0.01). Conclusion: High-intensity interval training improves glycaemic control but has limited effect on cardiovascular autonomic regulation in patients with type 2 diabetes.