Effects Of Fatigue Protocol On Biomechanics Of Lower Extremity In Stretch-shortening Cycle Movement

PurposeTo explore the effect of fatigue intervention on biomechanics of lower extremity and performance during a drop jump?DJ?task on the sports performance,kinematics,joint moment and power,so as to characterize the effect of fatigue on SSC movement performance from the perspective of stiffness and joint work/energy characteristics and explore the mechanics law of lower limb and its internal relations.MethodsThree-dimensional kinematics?Vicon,120 Hz?and Kistler force plates?Kistler,1200Hz?were used to collect sagittal plane kinematics and ground reaction force data synchronously of a total of fifteen trained male athletes during drop jump at 60cm height under pre-and post-fatigue conditions with shuttle running+vertical jumping fatigue protocol.The fatigue protocol required participants to complete five consecutive countermovement jumps?CMJs?with their best efforts after a group of shuttle running?6×10 m?.The subjects repeated the above sequence until the average height of 5 consecutive CMJs was below 70%of the individual maximum jump height.Paired-samples t-tests were used to evaluate the effects of fatigue protocol on the variables of interest including joint angle,moment,power,work and stiffness.The criterion?level was set to 0.05.Results1)For kinematics,the maximum height of DJ decreased in fatigued conditions?p<0.05?;while the touchdown angle and the range of motion????of knee and ankle joints increased?p<0.05?;Also,the occurrence time for eccentric,concentric and total phase increased?p<0.05?.Only the maximum flexion angular velocity of knee reduced?p<0.05?after fatigue.Besides,maximum push-off angular velocity of hip and knee reduced?p<0.05?under fatigue condition.2)For kinetics,only the maximum push-off moment and power of knee reduced in fatigue conditions?p<0.05?.Meanwhile,the stiffness of knee and ankle joint during the eccentric phase were reduced as well as leg stiffness?p<0.05?;3)For the joint work,the energy absorption and net energy of the ankle joint decreased during the DJ task compared with pre-fatigue condition;Also,the energy contribution of knee joint(C_knee)decreased during the eccentric phase of a DJ task?p<0.05?.ConclusionThe biomechanics of lower extremity changed under fatigue protocol intervention,indicating that fatigue changed the movement pattern,decreased control ability of the lower extremity especially the knee and ankle joint and further decreased sport performance.It is suggested that strengthening muscles of the above joints is essential to ensure the effect of long term Stretch-Shortening Cycle?SSC?training.In addition,the decreases of corresponding energy and the leg stiffness attributed to a decline in joint stiffness may be used as sensitive indexes to indicate the performance of drop jump in a fatigue condition.