Research On The Influence Of Different Degrees Of Fatigue On The Biomechanical Characteristics Of Lower Limbs At The Moment Of Landin

Research background and purpose: Landing is a common action in sports,and the impact force generated by the ground on the human body during jumping and landing can reach 2-10 times the body weight.The strong impact force and its transmission on the musculoskeletal system are the main reasons for sports injuries.For example,about 70% of sports induced ACL injuries occur without direct physical contact between athletes,but during deceleration or landing,due to the knee joint being subjected to greater force or torque during the movement,exceeding the limit load that the anterior cruciate ligament(ACL)can withstand,i.e.non-contact ACL injury.And in the later stages of the competition,the probability of sports injuries is higher.Nowadays,research generally believes that non contact ACL injuries in sports that occur in the later stages of competitions are usually related to fatigue.This study constructs fatigue models with varying degrees of grading for the human body through a fatigue intervention program of turn back running and vertical jumping,exploring the biomechanical strategy adjustment rules of the human body after fatigue,as well as the relationship between biomechanical indicators and ACL injury,in order to provide reference basis for preventing ACL injury and guiding public fitness.Research method: 20 healthy male college students were selected as the research subjects,and a fatigue intervention plan of turn back running and vertical jump was adopted.The maximum vertical jump height attenuation rate was used as the fatigue judgment standard.When the vertical jump attenuated to 80%,it was considered moderate fatigue,and when the maximum vertical jump attenuated to 70%,it was considered severe fatigue.The subjects completed three effective dual leg landing tests in non fatigue(NF),medium fatigue(MF),and severe fatigue(SF)states,using a quality motion capture system consisting of 16 infrared high-speed cameras and a kistler force measurement platform for synchronous data collection.SPSS22.0software was used to conduct one-way repeated measurement variance analysis to evaluate the differences in kinematics,dynamics,lower limb stiffness and lower limb work of landing in three fatigue states.Research result 1.Effect of fatigue intervention: There were extremely significant differences in the maximum heart rate and RPE scale scores of subjects in both SF and MF states.2.kinematics characteristics: the change of hip flexion angle in SF state was significantly lower than that in MF state(p=0.041),and the knee flexion angle in MF state was significantly higher than that in NF state at the time of touchdown(p=0.034);In terms of changes in joint angle,there was a significant difference in the changes in knee joint flexion angle between NF and MF and SF states(p=0.017,p=0.040);The knee joint flexion angle at the peak moment of ground reaction force in the MF state is significantly lower than that in the NF state(p=0.020);The second peak loading time of ground reaction force significantly increased in the MF state compared to the NF state(p=0.045).3.Dynamic characteristics: GRF2 and LR2 in SF state are significantly higher than those in NF state(p=0.030,p=0.042);The peak extension torque of the knee joint in the MF state significantly decreased compared to the NF state(p=0.011);The plantar flexion moment of the ankle joint in the MF state significantly increased compared to the NF state(p=0.045),while the peak plantar flexion moment of the ankle joint significantly decreased from the MF state to the SF state(p=0.037).4.Lower limb stiffness and lower limb work: When the MF state to the SF state,the plantar stiffness significantly increased(p=0.023);The joint stiffness of the knee joint significantly decreased from the NF state to the MF state(p=0.049),and the ankle joint stiffness significantly decreased from the NF state to the MF state.(p=0.01);The value of negative work done by the knee joint significantly increases during the MF to SF stages.(p=0.038).Conclusion: 1.The biomechanical changes in the lower limbs of the subjects during landing tasks are influenced by the degree of fatigue.After moderate fatigue,the landing biomechanical strategy is adjusted,resulting in a "soft landing" trend in the movement strategy.2.After severe fatigue,the movement strategy of the subjects during landing showed a trend of "hard landing".It may be an important reason for the increased risk of lower limb joint injury.