The Effects Of Lower Limb Asymmetry On Landing Posture Control

Purposes:The purpose of this study was to investigate the effect of asymmetry of the lower limbs on landing stability and the posture control.Methods:30healthy male subjects were randomly selected from the Sports department of University,22.8±1.7years old, height176.2±5.2cm, weight71.6±8.5Kg; subject with a history of lower extremity injury was excluded. The strength of subjects were measured by the Con-trex multi-joint strength-testing-system. Isokinetic muscle strength of knee joint was tested in concentric and eccentric mode at180°/s. The strength of lower limbs are used to evaluate lower limb asymmetry and the asymmetric group was defined as the symmetry index greater than10%, the index less than10%for the symmetric group. Subjects were asked to land on the floor without initial velocity from three heights(20cm,40cm,60cm)with hands on his hip. The methods of landing included landing with left foot、right foot and both feet. Subjects were asked standing on the force platform stably for2s after landing. Infrared Vicon motion capture system was used to record kinematics data and synchronized kistler force platforms were used to collect ground reaction force data and kinetic data.Results:①There are no significant differences between asymmetric group and symmetric group on kinematic and dynamic indexes between left and right lower limbs when drop landing from20cm,40cm,60cm heights. There is significant difference on between limbs’knee sagittal plane minimum angle between symmetry group and asymmetric group and the difference is greater than the symmetric group, There are no significant differences of other index②There are significant differences between the both limbs on the standardized DPSI when landing with single leg from20cm and TTS when landing from40cm and the parameter of non-dominant is bigger than the dominant. There is significant difference between the both limbs on the height of center of gravity and lower extremity stiffness when landing with single leg from20cm. There is a significant difference between limbs’ standardized DPSI on symmetry group and the center of gravity of the moving height on asymmetric group, the difference of standardized DPSI and gravity of the moving height increases with the increase of the height.③There is significant difference between the both limbs on the standardized Fz when landing with both legs from20cm, and the parameter of non-dominant is smaller than the dominant. There are significant differences between the both limbs on the minimum angle of the ankle coronal plane when landing with both feet from40cm、60cm and the peak velocity of ankle sagittal angular when landing from40cm. The parameters of non-dominant are smaller than the dominant. When falling to the ground with both feet, there is no significant difference between symmetric and asymmetric group at each index with the increase of height. Conclusions:①When human body falling from a certain height, according to the lower limb knee extensor strength distinguish between asymmetric and symmetric group,the difference of minimum sagittal knee angle is bigger than symmetry group between asymmetric limbs. The difference of symmetry limb between left and right on the landing stability, buffering capacity and the ability of posture control have no significant difference with the difference of asymmetry limb.②When human body falling from a certain height, by adjusting the stiffness of lower limb, center of gravity move height, TTS, the ground reaction force, non-dominant side body use different buffer strategies to maintain the dynamic stability of the body and buffering capacity, and the dynamic stability of the non-dominant side and buffering ability show stronger than dominant side, non-dominant side may have smaller risk of damage in actual movement process,the injury risk of dominant side especially of ankle joint is greater than the non-dominant side.③When human body falling from different heights, with the increase of height, the difference of buffer capacity and stability between left and right is bigger. Athletes can through power practice to reduce the differences of limbs to reduce the probability of damage.When people landing with both feet,due to the mutual compensation mechanism between limbs, there is no significant difference of all the indicators between limbs.④Because the small sample size of this study, the differences showed no regularity. Future research can increase the sample size and use the action strategy close to the actual movement to reflect the effects of lower limb asymmetry on landing.