Study design
muscular fitness [countermovement jump
SECONDARY, RECRUITMENT
A randomized parallel controlled trial was adopted, with an 8-week exercise intervention period. After baseline testing, all children were randomly assigned to HIIE(n = 20) and MICE(n = 20) groups. Body composition (weight, BMI, percentages of body fat, fat and lean body mass) and several physical fitness components were assessed by investigator at baseline and after 8 weeks of exercise training at the same time with similar conditions, including muscular fitness [countermovement jump (CMJ) and 50-m sprint), and cardiovascular fitness [peak oxygen uptake (VO2peak), maximal aerobic speed, blood pressure, and HRmax]. The body composition was primary outcome, while cardiovascular fitness and muscular fitness were secondary outcome.Before the training, the children were assessed in two parts separated by 1 day on weekends. The first part involved body composition and graded cardiovascular fitness evaluations, and were carried out in a warm cardiovascular fitness test laboratory located in the Capital University of Physical Education and Sports. Second, the measurement of muscular fitness, Yo-Yo intermittent endurance test and training intervention were completed in the track and field of children’ school. The post-test was performed two days after the last session, and all children should complete each assessment according to the previous sequence in their free time on weekends. All children have completed at least 80% of the minimum requirements of the training sessions for inclusion in the data processing. The training protocol was approved by the Ethics Committee of the Capital University of Physical Education and Sports (Approval NO. CUPES-2018-10-15-01) in accordance with the Declaration of Helsinki. The current study design, conduct and data analysis of this trial follow the recommendations of the CONSORT statement (see Fig. 
Flow chart depicting participant recruitment, randomized grouping and final analysis