Interval training in school settings has been shown to improve adolescent physical fitness; however, the optimal work-to-rest ratios (WRRs) for maximizing benefits across various fitness components remain unclear. This study aimed to assess the impact of school-based interval jump rope training (IJRT) with three different WRRs on physical fitness in adolescents aged 12 to 14 years and to identify the most effective WRRs. A cluster randomized controlled trial was conducted with 143 adolescents (mean age = 12.8 ± 0.5 years; 72 females) from a middle school in Shenzhen, China. Participants were randomly assigned to one of three groups based on their class: 30 seconds/30 seconds (G1, N = 48), 30 seconds/45 seconds (G2, N = 47), and 30 seconds/15 seconds (G3, N = 48) WRRs. Each group participated in IJRT three times per week for 8 weeks. Physical fitness parameters, including maximal oxygen uptake (VO_2max), grip strength, standing long jump, sit-ups, and 50-meter sprint performance, were measured pre- and post-intervention. Between-group differences were analyzed using analysis of covariance. The results demonstrated that the G2 (30 seconds/45 seconds) was more effective than the G1 (30 seconds/30 seconds) and G3 (30 seconds/15 seconds) in enhancing adolescents’ cardiorespiratory endurance and sprint performance.

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