Prediction of maximal vertical jump height with upper-limb countermovement, pre-jump knee-flexion and approaching distance in volleyball players

![CDATA[Rationale/Objectives: Maximal vertical jump height (MVJH) is one of the key determinant in the power of a spike in volleyball competitions. Upper-limb countermovement, pre-jump knee flexion, and approaching distance are three major factors affecting MVJH. However, the weighting of each factor remains unknown. This study aimed to establish a regression model of MVJH using parameters related to these three factors. Methods: Twenty male volleyball players (age = 31 8.44 years old) were recruited and they were asked to perform a series of maximal vertical jump tests with vertical challenger. Kinematics and kinetics data were collected using motion capture system, and MVJH was recorded by the vertical challenger. Peak vertical force (PF), shoulder peak extension angle (SAng) and angular velocity (SVel) from both arms, peak knee flexion angle (KAng) from both sides, BMI, and upper limb length (ULL) were calculated and these eight parameters were treated as MVJH predictors. Least absolute shrinkage and selection operator (LASSO) regression was applied to construct a model with the least number of predictors as well as the least root mean square error (RMSE). Results: Left SAng, left KAng, and approaching distance were identified as redundant factors and thus removed from the model. The coefficients of the final MVJH prediction model were: MVJH = 0.12 (right KAng) + 0.037 (right SAng) - 0.0011 (left SVel) + 0.0069 (right SVel) + 8.2691 (PF) – 0.78 (BMI) + 0.43 (ULL). The regression model has R-square equals to 0.609 (p < 0.05). Conclusions: This model provided weightings of different factors in predicting MVJH, which was associated with around 60% prediction accuracy. The results of this study could be tested in the future volleyball training aimed to increase MVJH.]]