Short-Term High-Intensity Interval Training Is Superior to Moderate-Intensity Continuous Training in Improving Cardiac Autonomic Function in Children

Abstract

<b><i>Objectives:</i></b> This study aimed to investigate the impact of 3 isocaloric exercise programs on cardiac autonomic nervous system (ANS) functioning in children. <b><i>Methods:</i></b> One hundred nine children (39% boys and 61% girls) aged 10–13 years (mean 11.07 ± 0.81) were conveniently assigned to 1 of 4 groups as follows: Moderate-intensity continuous training (MICT; <i>n</i> = 29) at 65–70% of the predicted maximum heart rate (MHR), High-intensity interval training (HIIT; <i>n</i> = 29) at > 80% of the predicted MHR, HIIT and MICT combined on alternate weeks (ALT; <i>n</i> = 27), and a control group (<i>n</i> = 24). Morning ANS activity was assessed via analysis of heart rate variability (HRV), with the patient in supine position for 10 min, before and after the exercise intervention. <b><i>Data Analysis:</i></b> A 2-way analysis of variance was used to evaluate the effects of training on all HRV parameters (<i>p</i> < 0.05/4 = 0.0125). <b><i>Results:</i></b> After 5 weeks of training, significant improvements were observed for ln of the standard deviation of normal-to-normal intervals (<i>p</i> < 0.0001), ln of the root mean square of successive difference (<i>p</i> < 0.0001), and ln of standard deviation 1 (<i>p</i> < 0.0001), with superior results reported in the HIIT group (effect size [ES] = 2.22, 2.69, and 2.69) compared with the MICT (ES = 1.67, 1.75, and 1.75) and ALT (ES = 0.87, 1.06, and 1.06) groups, respectively. <b><i>Conclusion:</i></b> Short-term HIIT seems to induce superior alterations in cardiac ANS activity compared to MICT and ALT in children through enhanced vagal activity.