This study examined anthropometric and fitness profiles of Japanese female professional baseball players and investigated the relationship between players' physical fitness and in-season game performance. Fifty-seven players who were registered in the Japan Women's Baseball League (JWBL) participated. Height, weight, grip strength, back strength, knee-extension and -flexion strength, hamstring extensibility, vertical jump height, and horizontal jump distance were measured at pre-season (February and March) in 2013. Game performance during the 2013 season (March to November) was obtained from official JWBL statistics. Vertical jump height showed significant positive correlations with individual performance records [e.g., total bases (r = 0.551), slugging percentage (r = 0.459), and stolen bases (r = 0.442)]. Similar relationships were observed between horizontal jump distance and performance statistics in most cases. In contrast, grip, back, and lower-limb strength, and hamstring extensibility were not significantly correlated with game performance. Stepwise regression analysis selected vertical jump height as an independent variable, significantly correlating with several game performance measures (e.g., total bases: adjusted R2 = 0.257). Also, vertical jump height and body mass index were identified as independent variables significantly associated with stolen bases (adjusted R2 = 0.251). Maximal jump performance, rather than simple isometric muscle strength or flexibility, is a good performance test that can be used at the end of pre-season to predict in-season batting and stolen base performance. Our findings demonstrate the importance of constructing pre-season training programs to enhance lower-limb muscular power that is linked to successful in-season performance in female baseball players.
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