The children included in the experimental group will make 10 weeks of aerobic training. The intensity of the race will be based on individual speed obtained in the last stage completed the progressive test, known as the maximal aerobic speed (MAV) in km/h. The running speed of the exercise protocol will be minimum 80% of the MAV in the protocol of continuous training. The intermittent progressive training is n * (10*15 s) to 100% MAV, and n from 2 to 6 series between the first and tenth week. The training protocol was adapted from previously described (Mandigout et al, 2002, Gamelin et al, 2009.). Acceptance of the exercise in a pediatric population has been previously observed by pilot study.

Will be included 160 children, 80 in an experimental group and 80 in a control group of both genders. The experimental group will realize aerobic training during 10 weeks (3×40min week-1; intensity, >80% maximal aerobic velocity - MAV), while the control group will have involved with the physical education classes two times a week for 50 minutes each class. The aerobic protocol will be composed by 2 sessions of intermittent running and 1 session by continuous.

The cardiac autonomic modulation of the sinoatrial node will be estimated via heart rate variability (HRV) pre- after 5 weeks - post-10 weeks of training and after 8 weeks of finished the intervention (follow-up period). The duration of the RR interval recordings (RRinterval) will be obtained from each children using a portable heart rate monitor (Polar RS800) at a sampling rate of 1000 Hz. The recordings will be downloaded via commercial software and export for later analysis of time and frequency domain measures of HRV. The time domain indices examined will be: the mean RR interval, the root-mean-square difference of successive normal RR intervals (RMSSD), which reflects vagal modulation, and the standard deviation of all normal RR intervals (SDNN), which comprises both sympathetic and vagal cardiac modulations (Task Force, 1996).