High-Intensity Interval Training: competitive and non-competitive effects on physical fitness in school adolescents

Introduction: Adolescents commonly do not reach vigorous-intensity physical activity guidelines, and physical education (PE) classes provide a key opportunity to promote adherence to WHO recommendations. Objective: The study aimed to determine the effects of a high-intensity interval training (HIIT) intervention with a competitive component compared with non-competitive HIIT and a control group on adolescents’ physical fitness. Methodology: A total of 199 students (93 females), aged 15–17 years, participated in a 10-week school-based intervention conducted in two public secondary schools in Mallorca, Spain. Physical fitness was assessed through cardiorespiratory fitness, lower- and upper-body strength, jump performance, waist circumference and body mass index. Results: The competitive HIIT group, implemented through a weekly ranking system, did not show significant pre–post improvements in any physical fitness variables. In contrast, the non-competitive HIIT group demonstrated substantial gains in muscular strength (+2.8, p < 0.001) and jump performance (+5.0, p = 0.011). The control group showed significant improvements in cardiorespiratory fitness (+1.7, p < 0.001), muscular strength (+1.3, p = 0.035), and waist circumference (–1.2, p = 0.006). Discussion: The present results align with previous studies highlighting the benefits of HIIT in school settings, suggesting that competitive elements may require more engaging motivational strategies than a simple ranking system to enhance adherence Conclusions: HIIT can effectively improve adolescents’ physical fitness in school settings, but competitive dynamics need careful design to maximize motivation and participation. Future research should explore innovative, context-specific strategies incorporating task variety and motivational factors.