## 4 Discussion  
The purpose of this study was to investigate the influence of running-induced fatigue on performance and lower limb biomechanics of the countermovement jump. Different from our assumptions, jump height was not significantly affected by running-induced fatigue. However, the kinematics and kinetics of the lower limbs, as hypothesized, were significantly changed due to fatigue, especially the kinematic parameters. No significant differences were found in the jump height between pre- and post-fatigue conditions. It seems that running-induced fatigue does not influence jumping performance. In previous studies, \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Phase** & **Condition** & **PVGRF(BW)** & \(p\) & ES \\ \hline \multirow{2}{*}{Push-off} & Pre & \(1.23\pm 0.13\) & \multirow{2}{*}{0.17} & \multirow{2}{*}{0.48} \\  & Post & \(1.30\pm 0.16\) & & \\ \multirow{2}{*}{Landing} & Pre & \(2.38\pm 0.79\) & \multirow{2}{*}{0.88} & \multirow{2}{*}{0.03} \\  & Post & \(2.36\pm 0.50\) & & \\ \hline \hline \end{tabular} _Notes:_ Pre: pre-fatigue; Post: post-fatigue; PVGRF: peak vertical GRF; \(p\): \(p\)-value; ES: effect sizes.  
\end{table} 
Table 4: Peak value of vertical ground reaction forces (GRF) in the push-off phase and landing phase. Figure 5: The joint moments between pre- (red solid lines) and post-fatigue (blue solid lines) during the landing phase. Shaded areas mean standard deviation. Black dotted boxes indicate significant differences between the two conditions. vertical jump height has been shown to be related to fatigue levels [29]. The fatigue protocols used previously focused on the fatigue of the knee extensor. The interpretation may be that the reduced strength of the knee extensor influenced the lower vertical jump height achieved. Knee extensor fatigue influences several biomechanical variables during countermovement jumping, whereas the fatigue of the knee flexor did not alter the kinetics and kinematics of the lower extremities [37]. The biomechanical alternations in the lower limbs caused by fatigue were varied, which might partly be due to the different fatigue levels and protocols. A decrease in vertical jump height was observed using a fatigue protocol in one hundred drop jumps [38]. However, fatigue induced by running, as a long-term fatigue protocol, may not be severe enough to fatigue the localized muscles which play a vital role in jumping performance. Consecutive jumps were used as a fatigue protocol in a previous study, which focused on landing biomechanics instead of jump height and the entire jump process [26]. Further research used two different exercise-induced fatigue protocols, one of which required running at a constant speed until subjects could not continue. In that study, only the landing phase was considered [39]. Our study focused on the effects of running-induced fatigue on jump height and the entire physiological process of the countermovement jump. Whether during the push-off phase or the landing phase, the main changes in kinematics happened in the frontal plane. Furthermore, the knee joint angle increased, whereas the hip joint angle decreased. During the push-off phase, the sagittal-plane of motion of the ankle joint decreased following the fatigue intervention, which may be indicating that the movement of the ankle joint was limited. As the triceps surae muscles are proposed to be related to ankle power generation and gait pattern during the push-off phase, the reduction in the triceps surae muscular strength caused by fatigue might be responsible for the ankle kinematics changes in this study [13]. This change would hamper the force production of the lower limbs as well as vertical jump performance [40]. In the final period of the push-off phase, the peak inversion angle under the fatigue condition was larger than that before fatigue, and the foot was in plantar flexion. Combining these changes, the risk of ankle injuries was increased under the post-fatigue condition [41].