the effects of low-volume highintensity interval versus moderate intensity continuous training on heart rate variability, and hemodynamic and echocardiography indices in men after coronary artery bypass grafting: a randomized clinical trial study

Background:heart rate variability (hrv) declines after coronary artery bypass grafting (cabg). the purpose of this study was to evaluate the effect of low-volume high-intensity interval training (lv-hiit) and moderate-intensity continuous training (mict) on hrv as well as, hemodynamic and echocardiography indices.methods:forty-two men after cabg (55.12 ± 3.97 years) were randomly assigned into lv-hiit, mict, and control (ctl) groups. the exercise training in lv-hiit consisted of 2-minute interval at 85-95 percent of maximal heart rate (hrmax), 2-minute interval at 50% of hrmaxand 40-minute interval at 70% of hrmax in mict for three sessions in a week, for 6-weeks. hrv parameters were evaluated by 24-hour holter electrocardiography (ecg) recording, and echocardiography parameters at baseline and end of intervention were measured in all 3 groups.results:at the end of the intervention, left ventricular ejection fraction (lvef) significantly increased in lv-hiit group (58.53 ± 7.26 percent) compared with mict (52.26 ± 7.91 percent) and ctl (49.68 ± 7.27 percent)groups (p < 0.001). furthermore, mean r-r interval, root mean square successive difference (rmssd) of r-r interval, and standard deviation of r-r interval (sdrr) in lv-hiit group considerably increased compared with mict group (p < 0.001). high-frequency power (hf) significantly increased in lv-hiit and mict groups compared with ctl group (p < 0.001). on the other hand, low frequency (lf) and lf/hf ratio significantly decreased in lv-hiit group in comparison with mict group (p < 0.010).conclusion:these results suggest that lv-hiit has a greater effect on improvement of cardiac autonomic activities by increasing r-r interval, sdrr, rmssd, and hf, and decreasing lf and lf/hf ratio in patients after cabg.