Pediatric obesity is associated with a decrease in cardiac autonomic modulation and baroreflex sensitivity. Physical activity increases heart rate variability in adults, yet no study has elucidated the mode and intensity of exercise for beneficial effects on cardiac autonomic modulation in children. Objective: The purpose of our study was to examine the effectiveness of 4 and 8 weeks of supervised, play-based activity on blood pressure, heart rate variability and baroreflex sensitivity in

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... lescents. Methods: Twenty-two recreationally active overweight, 8 to 12 year-old children were randomly divided into a 4and 8-week activity group and an unsupervised control group (4w, n = 6, 8w, n = 6, and C, n = 10). 4w and 8w groups performed play-based activities 5 days per week, 4 hours a day while C group were instructed to maintain a regular summer break with no supervised intervention. Heart rate variability and baroreflex sensitivity were tested before and after exercise with a heads-up tilt test. Results: Systolic blood pressure was significantly lower in all three groups in post conditions (P = 0.02, eta2 = 6.86). Normalized low and high frequencies reported a significant group-by-time difference in both supine resting conditions and after heads-up tilt (P = 0.04, eta2 = 0.28 and P = 0.05, eta2 = 0.28, respectively) and total power in supine position (P = 0.04, eta2 = 0.29) between the 8w, and the 4w and C groups, while baroreflex sensitivity increased by only 3 ms/mmHg in the 8w group (P = 0.09). Conclusion: 8 weeks of supervised, play-based physical activity improved autonomic nervous system activation with favorable changes in sympathovagal balance in recreationally active overweight preadolescents during summer break.