# Dynamic Characteristics of Approach Spike Jump Tasks in Male Volleyball Players
## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c} \hline  & & \(r\) (\(p\)-Value of & & \(r\) (\(p\)-Value of & & \\  & **RSJ-2L (SD)** & **Correlation** & **RSJ-1L (SD)** & **Correlation** & \(p\)-Value of & \\  & & **Coefficient)** & & **Coefficient)** & **t-Test** & **Cohen’s \(d\) (95\% CI)** \\ \hline Landing time (s) & 0.16 (0.02) & 0.498 (0.143) & 0.17 (0.02) & \(-\)0.196 (0.587) & 0.365 * & 0.291 (0.16, 0.18) \\ Push-off time (s) & 0.16 (0.01) & 0.479 (0.161) & 0.14 (0.02) & \(-\)0.619 (0.056) & 0.043 * & 0.745 (0.14, 0.16) \\ Support time (s) & 0.32 (0.03) & 0.587 (0.074) & 0.31 (0.04) & \(-\)0.427 (0.218) & 0.299 * & 0.347 (0.30, 0.34) \\ Peak ground & 1.63 (0.28) & \(-\)0.360 (0.307) & 3.00 (0.47) & 0.055 (0.880) & \(<\)0.001 * & 3.805 (1.94, 2.68) \\  & & \multicolumn{4}{c}{Peak joint moment (Nm/BW)} & \\ Ankle & 0.24 (0.03) & 0.024 (0.948) & 0.31 (0.03) & \(-\)0.064 (0.861) & \(<\)0.001 * & 3.199 (0.25, 0.29) \\ Knee & 0.35 (0.05) & 0.062 (0.865) & 0.53 (0.14) & 0.208 (0.564) & 0.001 * & 1.667 (0.38, 0.50) \\ Hip & 0.15 (0.42) & \(-\)0.016 (0.965) & 0.26 (0.46) & 0.065 (0.858) & \(<\)0.001 * & 2.561 (0.17, 0.23) \\  & & \multicolumn{4}{c}{Peak leading power (W/BW)} & \\ Ankle & \(-\)3.71 (1.84) & 0.334 (0.346) & \(-\)3.27 (1.29) & 0.492 (0.149) & 0.204 & 0.429 (\(-\)4.22, \(-\)2.76) \\ Knee & \(-\)13.46 (3.77) & \(-\)0.565 (0.089) & \(-\)12.83 (4.77) & 0.172 (0.635) & 0.725 & 0.113 (\(-\)15.11, \(-\)11.18) \\ Hip & 0.77 (0.53) & \(-\)0.013 (0.972) & 1.28 (0.98) & 0.529 (0.116) & 0.217 & 0.445 (0.63, 1.40) \\  & & \multicolumn{4}{c}{Peak push-off power (W/BW)} & \\ Ankle & 11.06 (2.03) & 0.270 (0.451) & 10.31 (2.09) & \(-\)0.294 (0.410) & 0.289 & 0.358 (9.73, 11.64) \\ Knee & 13.78 (3.45) & 0.567 (0.087) & 14.65 (3.79) & 0.074 (0.839) & 0.319 & 0.334 (12.55, 15.88) \\ Hip & 0.94 (0.61) & 0.032 (0.930) & \(-\)1.67 (0.81) & \(-\)0.194 (0.591) & \(<\)0.001 * & 3.458 (\(-\)1.07, 0.34) \\  & & \multicolumn{4}{c}{Joint stiffness (Nm/deg)} & \\ Ankle & 12.8 (6.9) & \(-\)0.033 (0.928) & 37.6 (16.3) & \(-\)0.539 (0.108) & 0.001 * & 2.319 (10.22, 39.38) \\ Knee & 6.1 (1.8) & \(-\)0.096 (0.792) & 12.0 (3.0) & 0.344 (0.330) & \(<\)0.001 * & 2.442 (3.58, 8.22) \\ Hip & 27.9 (16.9) & 0.383 (0.275) & 28.3 (13.4) & \(-\)0.631 (0.050) & 0.070 & 0.020 (\(-\)13.93, 14.73) \\ \hline \end{tabular}  
* Indicates significant difference found between the RSJ-1L and RSJ-2L, \(p<0.05\). \(r\): correlation coefficient of jump height. The positive value of power represents power generation, while the negative value of power represents power absorption.  
\end{table} 
Table 2: The landing, push-off, support time, peak GRF, and joint kinetic variables of the left leg and their correlation with the jump height during the spike jumps. current study were just 2.93 m/s and 2.50 m/s to reach 0.54 m and 0.35 m jump height, respectively, which were lower than those of the national level volleyball players found by [PERSON] et al. [1] The college-level players still have some room to improve their approach run velocity. Previous studies reported that fast and high loading movement prior to a jump can induce high muscle preactivation and stretch reflex [23; 24], and further increase the following muscle activation to result in the later improved performances [25; 26]. The approach running was likely to increase the activation of the lower extremity muscles [8]. Furthermore, the muscle preactivation was proved to be positively correlated with the joint stiffness [24; 27] that was crucial for the jumping performance [10; 14] or injury prevention [27]. In the current study, the RSJ-1L demonstrated greater approach run velocity, ankle and knee joint stiffness than the RSJ-2L, which could infer that the RSJ-1L induced higher ankle and knee muscle preactivation and activation of the lower extremity than the RSJ-2L. Moreover, due to the difference of take-off method and approach velocity, the RSJ-1L demonstrated greater peak vertical ground reaction force than the RSJ-2L in the current study.