Introduction: Badminton-specific agility, characterized by frequent lunges performed with the leg on the racket-holding side, is a key determinant of overall badminton performance. Although leg extension strength is expected to play a significant role, the factors that influencing badminton-specific agility remain unclear. This study therefore aimed to test the hypothesis that knee extension strength is correlated with badminton-specific agility in world-class and elite/international-level badminton players. Methods: This study included twenty-seven male and twenty-three female professional badminton players from the Japanese national team. Participants completed two tests: (1) a badminton-specific agility test measuring the time required to reach sensors at the four corners of a singles court using badminton-specific movement, and (2) an isokinetic knee extension strength test at angular velocities of 60 °/s and 180 °/s. The Spearman rank-order correlation coefficients were used to assess the relationships between them (P < .05). Results and discussion: Significant inverse correlations were found between knee extension torque normalized to body mass for the leg opposite the racket-holding hand and badminton-specific agility at both 60 °/s and 180 °/s (males at 60 °/s: rs = -.619; 180 °/s: rs = -.579; females at 60 °/s: rs = -.445; 180 °/s: rs = -.446). In contrast, only the same-side leg at 60 °/s showed a significant inverse correlation (males: rs = -.413; females: rs = -.490). Overall, these results show that knee extension strength is crucial for badminton-specific agility among world-class and elite/international-level male and female badminton players. Furthermore, our findings suggest differing demands for force production between the legs on the same and opposite sides of the racket-holding hand.
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