Effect of high intensity interval training on heart rate variability in type 2 diabetic patients

The purpose of this study was to examine the effect of high intensity interval training (HIIT) on cardiovascular autonomic function as determined by heart rate variability (HRV), in type 2 diabetic patients. Fourteen type 2 diabetics (Mean age ± SD = 57±6.71 years) and five aged matched controls participated in the study. Body weight, body height, body composition, resting blood pressure, resting heart rate, waist and hip circumferences were measured at baseline and at the end of the study. Participants were required to self test their glucose levels (fasting glucose) before the initial assessment as well as at the end of the study. Resting electrocardiogram (EKG) was measured at baseline and 12-weeks after training. HRV was assessed manually from calculation of the mean R-R interval and its standard deviation measured on a 5-min EKG. Type 2 diabetic participants followed a 12-week HIIT on a treadmill consisting of four 30 min sessions per week. A HIIT session involved a 3-minute warm-up period, several short (2-min), maximum-intensity (80-90%) efforts separated by moderate intensity (50-60%) recovery intervals (2-min) and a 3-minute cool down period. Results demonstrated a significantly greater HRV pre compared to post training, t(13)=-7.46, p=0.0001. HIIT resulted in significant reduction of resting heart rate (RHR), systolic blood pressure (SBP), diastolic blood pressure (DBP), and fasting glucose levels. In addition, HIIT resulted in significant improvement in all body composition components. Mean weight, mean body fat and mean values for hip and waist circumferences were significantly lower after 12 weeks of training. The beneficial effect on autonomic regulation as reflected in increased HRV may have clinical importance in preventing sudden cardiac death in type 2 diabetes subjects. The adherence to the exercise program of the relatively inactive and obese diabetic population was good in this study, suggesting that guided exercise protocols may have clinical importance in the prophylactic treatment of type 2 diabetes subjects. More data in a large sample of type 2 diabetes patients are needed to confirm the beneficial effects of high intensity interval training on HRV.