The impact of four weeks of high intensity interval training oncardiac autonomic function in physically inactive males and females

Introduction: Physical inactivity is the fourth largest risk factor of premature mortality, responsible for 6% of deaths each year worldwide. Autonomic dysfunction has shown to be an indicator of cardiovascular diseases. High intensity interval training has shown to reduce traditional cardiovascular risk factors in less time than traditional aerobic exercise training. However, the adaptations following a high intensity interval training programme to the cardiac autonomic nervous system have not yet been fully researched.

Method: Using an independent-measures design, 45 physically inactive males and females (22.8 ± 2.7 years) were placed into either a high intensity interval training or control group. The subjects in the high intensity interval training group completed 3 x 30 seconds all out maximal cycle sprints, 3 times a week on a Wattbike cycle ergometer at a resistance of 7.5% of their body weight, with two minutes of active recovery between bouts, for four weeks. Cardiac autonomic function was measured using the task force monitor.

Results: This study found that four weeks of high intensity interval training led to resting heart rate significantly reducing (65.59 ± 10.15 to 63.05 ± 13.42 b.min-1; p < 0.05) and significant improvements in total power spectrum density (498.8 ± 239.8 ms2; p < 0.05) and high frequency power (389.4 ± 123 ms2; p < 0.01) against the control group. There was a nonsignificant increase in low frequency power (189.7 ± 91.2 ms2) and no significant reduction in LF/HF ratio compared to the control group.