Effects of the FIT FIRST Teen Multisport Program on Adolescents’ Physical Fitness and Well-Being: A Cluster Randomized Controlled Trial

Purpose: School-based physical education (PE) can counter declines in fitness in adolescence, yet scalable, curriculum-embedded fitness programmes are scarce. We evaluated the implementation of FIT FIRST Teen (FFT), a teacher-delivered, high-intensity multisport programme across one school year. Methods: A cluster randomised controlled trial was conducted in 22 Danish schools (FFT, n=517; Control, n=860). Teachers in FFT were trained via a 1-day course and a manual and delivered three 40-minute lessons/week. The primary outcome was cardiorespiratory fitness, assessed via the Yo-Yo Intermittent Recovery Level 1 Children’s test (YYIR1C). Secondary outcomes included handgrip strength, agility, balance, body composition, resting heart rate, and well-being. Multilevel modelling assessed the effectiveness of FFT, and exploratory latent transition analysis (LTA) was used to uncover latent fitness profiles and transitions over time in the two arms. Results: Compared with controls, adolescents allocated to FFT showed greater improvements in cardiorespiratory fitness, with a mean pre–post difference in YYIR1C distance of 106 m (p=0·009). In terms of secondary outcomes FFT showed greater gains in handgrip strength (~0.81 kg; p=0·012), and muscle mass (~0·44 kg; p<0.001). No intervention effects were observed in terms of well-being. Exploratory LTA supported a four-profile solution (high-fit, moderately-high-fit, moderately-low-fit, low-fit) and suggested that adolescents in the FFT group were more likely to remain in high-fit profile membership over time, compared to the control arm participants who tended to transition towards worse fitness profiles. Conclusions: Compared to the control arm, a 40-wk intervention with FFT improved cardiovascular fitness, handgrip strength, and muscle mass. FFT offers an alternative to PE curricula to improve adolescents' physical fitness.