Objectives To explore the effect of fatigue intervention on biomechanics of lower extremity and performance during the stretch-shortening cycle(SSC) movement-drop jumps(DJ).Methods The Vicon motion capture system and 3D Kistler force plates were used to collect sagittal plane kinematics and ground reaction force data synchronously of a total of fifteen trained male athletes under pre-and post-fatigue conditions with shuttle running + vertical jumping fatigue protocol.The joint angle,joint moment,power,work,and leg/joint stiffness were compared before and after fatigue.Results After fatigue,the maximum height of DJ decreased(P＜0.05),while the touchdown angle and the range of motion(△θ) of knee and ankle joints,as well as the occurrence time for the eccentric,concentric and total phase increased(P＜0.05).However,the maximum push-off moment and power of knee reduced(P＜ 0.05).The stiffness of knee and ankle joints during the eccentric phase reduced,resulting in the reduction of the leg stiffness(P＜0.05).Moreover,the energy absorption and net energy of the ankle joint decreased;meanwhile,the energy contribution of the knee joint decreased during the eccentric phase of a DJ task.Conclusion Fatigue changes the movement pattern,decreasing the control ability of the lower extremity especially in the knee and ankle joint,and results in decreased performance.Moreover,the decrease of leg,ankle and knee stiffness and the corresponding energy can be used as sensitive indexes to evaluate the performance of drop jumps in a fatigued condition.%目的:探讨疲劳干预对典型拉长-缩短周期动作(SSC)——落地反跳(DJ)的下肢生物力学和运动表现的影响.方法:采用Vicon及三维测力台同步采集15名田径专业跑、跳类专项男性运动员在折返跑+垂直纵跳疲劳干预前后落地反跳时的运动学及地面反作用力数据.比较疲劳前后的运动表现及下肢三关节运动学、动力学、刚度和关节做功等特征.结果:疲劳后,(1)DJ腾空高度下降(P＜0.05),膝、踝关节的触地角度和角度变化量以及向心期、离心期以及总触地时间均增加(P＜0.05);(2)膝关节的蹬伸力矩以及功率降低(P＜0.05);(3)膝、踝关节刚度下降,并引起下肢整体刚度下降(P＜0.05);(4)膝关节的能量吸收贡献度、踝关节的能量吸收以及净能量均下降(P＜0.05).结论:疲劳改变SSC动作结构,降低下肢尤其是膝、踝关节运动控制能力进而导致运动表现下降.此外,下肢及膝、踝刚度的下降,结合上述关节能量特征的改变,是进一步评价疲劳发展过程中SSC力学表现的重要参考.
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