Abstract：
There is a plethora of research attempting to contrast high- and low-velocity pitchers to identify traits to target for increasing velocity. However, pitch velocity exists on a continuum. Therefore, our purpose is to display the analytical discrepancies between creating velocity subgroups and leaving velocity as a continuous variable by examining the influence of ball velocity on elbow valgus torque. Motion capture data for 1315 actively competing pitchers were retrospectively extracted from a private database. We compared three analytic methods: (1) linear regression of valgus torque on ball velocity, (2) t-test between low- and high-velocity groups formed by a median split, and (3) t-test between very low- and very high-velocity groups formed by upper and lower velocity quartiles. Linear regression indicates ball velocity influenced valgus torque (p < 0.001, R2 = 0.280). Median splitting reduced the predictability of ball velocity on valgus torque (p < 0.001, R2 = 0.180). Conversely, extreme group splitting artificially inflated the effect size (p < 0.001, R2 = 0.347). We recommend sports biomechanics researchers not discretise a continuous variable to form subgroups for analysis because (1) it distorts the relationship between the variables of interest and (2) a regression equation can be used to estimate the dependent variable at any value of the independent variable, not just the group means.
摘要：
有大量的研究试图对比高速和低速投手，以确定提高速度的特征。然而,俯仰速度存在于一个连续体上。因此,我们的目的是通过检查球速度对肘部外翻扭矩的影响来显示创建速度子组和将速度作为连续变量之间的分析差异。从私人数据库中回顾性地提取了1315名积极竞争的投手的运动捕获数据。我们比较了三种分析方法：（1）外翻扭矩对球速度的线性回归，(2)中值分裂形成的低速和高速组之间的t检验，（3）由上下速度四分位数形成的极低和极高速度组之间的t检验。线性回归表明球速度影响外翻扭矩(p<0.001,R2=0.280)。中值分裂降低了球速度对外翻扭矩的可预测性（p<0.001，R2=0.180）。相反，极端群体分裂人为膨胀效应大小(p<0.001,R2=0.347)。我们建议运动生物力学研究人员不要离散连续变量来形成子组进行分析，因为（1）它会扭曲感兴趣的变量之间的关系，（2）回归方程可以用来估计自变量的任何值的因变量，不仅仅是团体的意思。
