The Influences Of Trunk Position On The Biomechanics Of Low Extremity During Bodyweight Squat

Purpose:Bodyweight squat training is often applied in rehabilitation programs for knee joint diseases,but incorrect way of squat training will increase the risk of patient injury,Changing technique will also affect the training effect.Developing a more proper and effective training pattern is still a problem that plagues the clinic.There is evidence that the position of the trunk can regulate the biomechanics of the knee joint in different exercises,but the specific effect of the position of the trunk on the biomechanics of the knee during bodyweight squat has not been studied.In this study,we set the position of the trunk as a single variable,using biomechanical research methods to explore the effects of trunk forward lower limb joint kinematics,dynamics,muscle activity,muscle force and joint load during bodyweight squat.Methods:Biomechanical analysis was performed on 12 healthy young college students who executed more forward leaning bodyweight squats and less forward lean trunk bodyweight squats both with knee flexion reach 90 °.We calculated the integral myoelectricity,joint angle and join moment of the lower extremity muscles in the ascending phase with the surface EMG signal acquisition and reverse dynamics algorithm.Combined with dynamic musculoskeletal simulation,the lower limb muscle strength and tibiofemoral joint compressive and shear force were estimated.The paired sample t-test was used to compare the difference in the muscle activity and the joint angle,the joint moment and the average muscle strength and joint load for every 5° change in knee joint angle between two modes.The significance level was?=0.05.Results:(1)During the ascending phase,more forward lean trunk increases the hip extension moment and the integral myoelectricity of the hip extensor muscle,reducing the knee extension moment and the integral myoelectricity of the quadriceps muscle.(2)The adjustment of the lower extremity muscle strength by more forward lean is significant.In the range of knee flexion about >85°,the force generated by the quadriceps decreases,and the maximum decrease is 1.32BW(p=0.001).In the range of knee flexion about>80°,the strength produced by the gluteus maximus increases about 0.44BW(p<0.001).In the range of knee flexion about >50°,the strength generated by the hamstring muscle is greater,and the maximum increase is 0.57BW(p<0.001)at the range of knee flexion within 75-70°;the strength of tibial anterior muscle decreased by about 0.05BW(p=0.001)at knee flexion of about 90°.(3)Compared with less forward lean trunk,the tibiofemoral joint compressive force at the peak of the knee flexion was reduced by 0.93BW(p=0.001);the peak tibiofemoral joint pressure force was reduced by 0.78 BW.(4)Bodyweight squat with more forward lean trunk and less forward leaning trunk only produced the posterior shear force of the tibiofemoral joint,and there was no difference between the two modes.Conclusions:(1)When do bodyweight squats by using the more trunk forward lean(about 45°)can reduce the activities of the knee muscle strength and the knee extension moment and increase the activities of the hip muscle strength and the hip extension,change joint dominant mode during ascending phase of squat.(2)The more forward lean trunk(about 45°)reduces the tibiofemoral joint compressive force at the maximum moment of knee flexion(knee flexion about90°),and peak tibiofemoral joint compressive force.(3)Bodyweight squat with trunk forward lean about 35°– 45° only produce the posterior shear force.(4)Clinical implications: Technical specifications should be ensured in the bodyweight squat training.For patients with insufficient quadriceps,the more forward lean trunk squat training can be selected;for patients with weak hip extensor,the less forward trunk lean squat is recommended.When the goal is to reduce tibiofemoral joint compressive force,it is recommended to use more trunk forward lean(about 45°)bodyweight squat training;when the goal is to reduce anterior tibiofemoral shear force,it is recommended to use forward trunk leaning(35°– 45°)bodyweight squat.