Experimental protocol
ExG
In this experiment, the subjects in the ExG group received jump rope training and special preparatory activities (JR + SPA) 3 times a week for 12 weeks, and the jump rope training content was forward double-legged alternating jump rope, backward double-legged alternating jump rope, double-legged alternating cross jump rope, and squatting alternating single-legged jump rope; the ConG received only the regular special preparatory activity (SPA) training content. During the preparation period, the subjects underwent 2 sessions of acclimatization training to facilitate familiarization with the training content and testing procedures, and after an interval of 1 day, all subjects were tested for dynamic balance and ball impact stability (pre-test). The program was continued for 12 weeks, and all subjects were tested for dynamic balance and ball impact stability (post-test) after an interval of 48 h. Because the subjects were trained for only 12 weeks of the microscopic macrocycle, which was relatively short, no interim tests were designed, which could hardly be the main factor influencing the experimental results even though the subjects were in a rapid growth phase, thus ensuring the validity of the experimental results. We paid special attention to the integrity and relevance of the experimental sessions and exercises throughout the training process to avoid youth sports injuries, and there were no cases of subjects dropping out of the experiment due to injury during the 12-week microscopic macrocycle training, and each training session was divided into three parts, the specific contents and schedule are shown in Table Experiment content and schedule table.Part I: Subjects in the ExG and ConG performed jogging and stretching exercises together for 10 min, the ExG performed RJ + SPA with 10 min of experimental content and 10 min of SPA content, and the ConG performed SPA training content only for 20 min.Part II: The same single technique and technique combination exercises. The single technique includes hitting the straight ball with the forehand, hitting the straight ball with the backhand, hitting the diagonal ball with the forehand, hitting the diagonal ball with the backhand. The technique combination exercises include hitting the straight ball with the forehand and hitting the diagonal ball with the backhand, hitting the straight ball with the forehand and hitting the straight ball with the backhand, for 80 min.Part III: The same stretching and relaxation exercises for 10 min.