Comparative analysis of isokinetic muscle function, anaerobic power, and physical fitness according to Asian BMI categories in youth male soccer players: a cross-sectional study

Background Body composition significantly influences athletic performance, with Body Mass Index (BMI) commonly utilized to guide training programs. This study evaluates isokinetic muscle function, anaerobic power, and physical fitness in youth soccer players based on Asian-specific BMI categories. Methods Seventy-five male youth soccer players were classified into Asian-specific BMI groups: normal weight (18.5–22.9 kg/m², n = 25), overweight (23–24.9 kg/m², n = 25), and obese (≥ 25 kg/m², n = 25). Assessments included body composition, isokinetic knee strength (60°/s), anaerobic power, and physical fitness tests. Statistical analysis was conducted using one-way ANOVA with Tukey’s post hoc tests. Results Overweight and obese players showed greater absolute knee strength ( p < 0.001–0.05) and anaerobic power ( p < 0.001) than normal-weight players, whereas no differences were observed in body weight–normalized strength or fatigue index ( p > 0.05). Obese players demonstrated greater back strength ( p < 0.05), while normal-weight players showed superior standing long jump performance ( p < 0.05). Conclusions Higher Asian-specific BMI categories were associated with greater absolute knee strength and anaerobic power in youth male soccer players, whereas body mass-normalized performance showed a different and less consistent pattern. These findings should not be interpreted as direct performance benefits of obesity because BMI does not distinguish between fat mass and lean body mass, and the higher-BMI groups also exhibited greater mean muscle mass and relatively low body fat percentages. Direct body composition measurements and both absolute and body mass-normalized performance indicators should therefore be considered alongside BMI when evaluating and designing conditioning programs for youth soccer players.