The purpose of this study was to test the hypotheses that in obese children: (1) hypocaloric diet (D) improves both heart rate recovery at 1 min (delta-HRR1) after an exercise test, and cardiac autonomic nervous system activity (CANSA) in obese children; (2) diet and exercise training (DET) combined leads to greater improvement in both delta-HRR1 after an exercise test and in CANSA, than D alone. Moreover, we examined the relationships among delta-HRR1, CANSA, cardiorespiratory fitness and anthropometric variables (AV) in obese children submitted to D and to DET. 33 obese children (10 +/- 0.2 years; body mass index (BMI) > 95th percentile) were divided into 2 groups: D (n = 15; BMI 31 +/- 1 kg/m2) and DET (n = 18; 29 +/- 1 kg/m2). All children performed a maximal cardiopulmonary exercise test on a treadmill. The delta-HRR1 or LF/HF ratio (p > 0.05). In contrast, the DET group showed increased peak VO2 (p = 0.01) and improved delta-HRR1 (delta-HRR1 = 37.3 +/- 2.6; p = 0.01) and LF/HF ratio (p = 0.001). The DET group demonstrated significant relationships among delta-HRR1, peak VO2 and CANSA (p < 0.05). In conclusion, DET, in contrast to D, promoted improved A delta-HRR1 and CANSA in obese children, suggesting a positive influence of increased levels of cardiorespiratory fitness by exercise training on cardiac autonomic activity.

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