Effects Of Fatigue And Sub-threshold Vibration On Biomechanics Of Knee Joint

Anterior cruciate ligament(ACL)is one of four major knee ligaments.ACL is an important structure to stable knee joint.ACL injuries are one of the most common ligament injuries in sports,which is often occur in cutting,sudden stops,pivoting or landing.Fatigue is considered to be a very important neuromuscular factor contributing to ACL injuries.Some statistical studies indicated that incidence of athletic injury occurring in the later stages of activities and competition is significantly higher.The study results of sub-threshold vibration noise in posture balance control and touch perception indicated sub-threshold vibration noise can enhance somatosensory feedback and perceive weaker signal.However,studies of whether sub-threshold vibration noise can decrease ACL injuries ware never done.Therefore,The First purpose of this study was to determine the effects of fatigue on the risk ACL injuries from the perspective of knee joint biomechanics,The Second purpose was innovatively explored the potential role of sub-threshold vibration noise in the prevention of ACL injuries.Thirty-two active male adults were participated in the experiment.Half of them completed landing and sudden cutting tasks with fatigue during sub-threshold vibration noise intervened and none sub-threshold vibration noise intervened,while the others completed the same tasks without fatigue during sub-threshold vibration noise interrupted and none sub-threshold vibration noise interrupted.Sub-threshold vibration noise was generated by micro motor vibration.The kinematics and kinetics data during experiments were measured by motion capture system of VICON and force plates of Bertec.By analyzing experiment data and synthesized fatigue and sub-threshold vibration noise,we can conclude some conclusions as follow:(1)Knee flexion angle was increased significantly when subjects with fatigue executed experiment tasks.Subjects attempted to decrease ACL injury risk by increasing knee flexion angle of landing to decrease impact from ground.(2)Knee rotation angle and rotation moment was increased significantly when subjects with fatigue executed experiment tasks.Previous studies indicated the larger knee rotation angle and rotation moment,the higher ACL loading.Knee rotation angle and rotation moment increased may as a result of fatigue affecting musculoskeletal system in turn decreasing the capability of the skeletal muscle to generate force production.In addition,fatigue contributed to posture control ability and body coordination decreasing may also increase knee rotation angle and rotation moment.(3)During the intervention of sub-threshold vibration noise group,knee vertical compression force of subjects with fatigue was significantly larger than subjects without fatigue.However,during the absence of intervention of sub-threshold vibration noise group,knee vertical compression force of subjects with fatigue was significantly smaller than subjects without fatigue.There are interactive effects between sub-threshold vibration noise and fatigue that may change activation of the muscle around knee joint during fatigue.(4)Sub-threshold vibration noise prevented ACL injuries in this study have not significant effects,expect initial contacted knee flexion angle and double stance peak knee flexion angle at without fatigue condition.Sub-threshold vibration noise may not be suitable for the prevention of ACL injuries,because ACL injuries often occur at high difficult and high intense sports,and the ability of sub-threshold vibration noise enhancing somatosensory feedback may be limited,which can't significantly change biomechanics of knee joint when executed these sports.