# Is knee extension strength a key factor in badminton-specific agility among elite players?

## TL;DR

This study shows that knee extension strength, especially in the non-racket leg, is strongly linked to agility in elite badminton players.

## Contribution

The study identifies knee extension strength as a key factor in badminton-specific agility, with differing leg demands.

## Key findings

- Strong inverse correlations were found between non-racket leg knee extension strength and agility in both male and female players.
- Same-side leg strength showed weaker but significant correlations, especially at lower angular velocities.
- Results highlight differing force production demands between the racket and non-racket legs in elite badminton players.

## Abstract

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.

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).

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.