Sex differences in ball velocity generated by kicking relative to sprint velocity in soccer players: A comparison of collegiate men and women and junior high school girls

Purpose: Women’s soccer is often perceived as lacking speed and intensity compared with the men’s game. Although sex differences in sprint performance and kicking ability have been reported, female players use a ball with the same specifications as in the men’s game from junior high school age onward. This study examined whether there are sex differences in the ratio of ball velocity generated by kicking to sprint speed in soccer players, to clarify whether identical ball specifications may constrain play speed at different developmental stages. Methods: Participants were 22 male collegiate, 21 female collegiate, and 18 female junior high school soccer players. After a standardized warm-up, participants performed a 30-m sprint, an inside kick, and an instep kick on an artificial pitch. Sprint speed was calculated from the fastest valid 30-m sprint trial. Ball velocity was determined using video analysis of successful kicking trials, and the mean of three trials was calculated after excluding the maximum and minimum values from five successful attempts. The ratio of ball velocity to sprint speed was calculated for both kicking conditions. One-way analysis of variance (ANOVA) was used to compare sprint velocity. For ball velocity and the ratio of ball velocity to sprint velocity, a mixed-design two-way ANOVA was conducted, with group as the between-subjects factor and kick type as the within-subjects factor. When significant effects were found, Bonferroni post hoc tests were applied. Results: Sprint speed and ball velocity were significantly higher in male collegiate players, followed by female collegiate players and junior high school players. No statistically significant difference was observed in the ratio of ball velocity to sprint speed between collegiate men and collegiate women for either kicking condition, but junior high school female players exhibited significantly lower ratios than both collegiate groups. Conclusion: These findings indicate that female collegiate soccer players are able to generate ball velocity proportional to their sprinting ability, despite lower absolute performance levels than male players. However, junior high school female players are unable to generate ball velocity commensurate with their sprint speed. This suggests that the use of adult-size balls is unlikely to substantially affect play speed in collegiate women’s soccer but may constrain it in junior high school women’s soccer.