Effects Of Different Grades Of Fatigue On Lower Extremity Biomechanics Of Stretch-shortening Cycle In Runners

Purpose: To investigate the effects of different grades of fatigue on the biomechanics of lower limbs of female runners,including the movement performance and the trend of the three joints of lower limbs,taking the typical "elongate-shorten cycle" movement — drop jump as the task.At the same time,the possible mechanism of lower limb injury and sensitivity index of exercise-induced fatigue were explored to reveal the internal relationship between lower limb mechanical law and injury.Methods: Qualisys motion capture and analysis system（6 infrared cameras）and Bertec three-dimensional force measurement platform were used to synchronically collect the kinematic and dynamic data of 15 female runners from Inner Mongolia Normal University during the landing rebound from 40 cm height during the fatigue intervention of 10×6m reentry +endeavor for 5 consecutive maximum longitudinal jumps.The fatigue run +jump process is defined as a round,participants were in fatigue intervention measure 5 times after each round of longitudinal slip average and and quiet,comparing the average vertical jump five times when calculating the vertical jump height attenuation;at the same time,fatigue self-sensing scale（RPE）and heart rate（HR）were used for auxiliary judgment,and the fatigue progression grade was divided into Non-fatigue（NF）,Medium-fatigue（MF）and Serious-fatigue（SF）.In addition,one-way an OVA was performed on the kinematics and dynamics data of the lower extremity three joints of the subjects under different fatigue levels to analyze the influence of fatigue on each variable parameter.The significance level α was set as 0.05,and the significance level was set as 0.01.Results: 1)For kinematics,compared with NF,MF significantly prolonged the centrifugal period and total touchdown time of the subjects’ landing rebound（P < 0.05）,significantly reduced the height of the flight（P <0.01）,and significantly increased the center of gravity displacement（P <0.01）;At the same time,the maximum flexion Angle and Angle change of the three joints were significantly increased（P < 0.05）,and the occurrence time of the maximum flexion Angle of the three joints was significantly prolonged（P< 0.05）.The angular velocity of ankle flexion increased（P < 0.05）,while the angular velocity of hip pedal extension decreased（P < 0.05）,and the time of hip and knee pedal extension was significantly delayed（P < 0.05）.Compared with MF,the height and center of gravity displacement in SF group were significantly reduced due to the significantly shortened take-off time（P <0.05）,and the centriptic period time was significantly prolonged（P < 0.05）.The maximum buckling Angle and Angle variation of the three joints of the lower limbs decreased,while the buckling angular velocity of the knee joint decreased significantly（P < 0.05）.2)For dynamics,with the deepening of fatigue,the peak value of vertical ground reaction force decreases first and then increases,while the front and rear components and the left and right components increase first and then decrease（P < 0.05）;The torque and power of the three joints of the lower limbs decreased gradually,and the decrease was most obvious at the knee joint（P < 0.05）,and the occurrence time of the maximum torque and power was significantly prolonged（P < 0.05）.The stiffness of knee and ankle joints decreased significantly at first and then increased,leading to the same change of lower limb stiffness（P < 0.05）.Conclusion: This study used the fatigue caused female runners intervention plans the biomechanics changes of ground bounce,show that in the process of fatigue deepening,the lower limb kinematics and dynamics of the change of the parameters in the nonlinear,its means of be born,there is from the "hard landing" to "soft landing" to the change of the "hard landing",It indicates that the movement structure changes of lower limbs will be different in different fatigue grades,and with the deepening of fatigue,the motion control ability of lower limbs,especially knee and ankle joints,will be reduced,and the risk of lower limb injury will be increased when women use rigid landing mode in severe fatigue.