Sex-Related Differences in Adolescent Physical Fitness, Physical Activity Levels and Enjoyment: A Two-Year Follow-Up of Italian Middle School Students

his two-year longitudinal study examined sex-specific changes and interrelations among body composition, physical fitness, physical activity (PA) enjoyment and PA levels during early adolescence. Methods: A cohort of 266 Italian middle school students (boys: n = 139; girls: n = 127) was assessed at two time points across two consecutive school years using anthropometry, field-based fitness tests, the Physical Activity Enjoyment Scale Questionnaire (Italian version) and a PA frequency questionnaire. Repeated-measures ANOVAs were used to explore time and time × sex effects, and correlations between change scores were calculated to explore associations between variables. Results: BMI increased in both sexes, while fat mass decreased in boys and increased in girls. Boys showed greater gains in cardiorespiratory fitness and muscular strength, whereas girls maintained better flexibility. Moderate PA and overall moderate-to-vigorous PA (MVPA) increased over time, with stronger positive associations between changes in PA enjoyment and MVPA in boys. Conclusion: These findings describe sex-specific patterns in physical fitness, body composition, and physical activity during early adolescence, and may help inform future research on sex-sensitive, individualized physical education approaches.