Ball velocity on the kick in futsal: comparison between youth with different performance levels and correlation of the predictive variables of performance

AbstractThe aim of this study was to compare and verify the possible correlations between ball velocity with foot velocity, knee angle and length of last stride between practitioners and non-practitioners of futsal game. Fourteen young males with aged between 13 and 15 years old divided into two groups: practitioners (G1) and non-practitioners (G2), according with the time of futsal structured practice. For the kinematic analysis we had used two cameras at a sampling frequency of 120 Hz, fixed laterally to the movement performed in order to focus the markers in the limb of kick. Each participant has performed ten kicks simulating a kick of ten meters in futsal. Three-dimensional data of the lower limb of kick were obtained in DVIDEOW software and treated in Matlab environment in order to obtain the variables of interest: ball velocity (VELBALL), foot velocity (VELFOOT), knee angle (ANGKNEE) and length of last stride (LLS). Statistically all data displayed higher levels in G1 compared to G2. In addition, no significant differences were found between trials in each group (p < 0.05). In G1 a multiple regression analysis revealed only influence on VELBALL 17% caused by LLS. Moreover, in G2 any variable have influenced VELBALL. However, we conclude that the variables are different between practitioners and non-practitioners of futsal game with aged between 13 and 15 years old, and the variable VELBALL could be little influenced by the LLS in this age band. Thus, we suggested that coaches maintain focus on development and monitoring this characteristic of movement, especially in novices, in order to identify players with different levels of performance of kicking in a futsal context.

摘要
本研究旨在对比并验证五人制足球（futsal）参与者与非参与者之间，踢球时的球速与足部速度、膝关节角度以及最后一步步长之间的潜在相关性。
本研究共招募14名年龄介于13至15岁的年轻男性，根据五人制足球系统训练时长分为两组：参与者组（G1）与非参与者组（G2）。
运动学分析采用两台采样频率为120Hz的摄像机，横向固定于动作侧方以清晰捕捉踢球肢体上的标记点。每位参与者完成10次模拟五人制足球10米距离的踢球动作。
研究采用DVIDEOW软件获取踢球下肢的三维运动数据，并在Matlab环境中进行后处理，以提取目标变量：球速（VELBALL）、足部速度（VELFOOT）、膝关节角度（ANGKNEE）以及最后一步步长（LLS）。
统计学分析结果显示，G1组的各项指标均显著高于G2组。此外，两组内部各次测试之间均未发现显著差异（p < 0.05）。
在G1组中，多元回归分析表明，最后一步步长（LLS）仅能解释17%的球速（VELBALL）变异；而在G2组中，无任何变量对球速（VELBALL）存在显著影响。
综上，本研究得出结论：13至15岁年龄段的五人制足球参与者与非参与者之间，上述变量存在显著差异，且该年龄段内最后一步步长（LLS）对球速（VELBALL）的影响较小。据此，我们建议教练员应重点关注并训练这类动作特征，尤其针对新手球员，以在五人制足球场景中甄别出踢球表现水平存在差异的运动员。