| Objective:Stair walking is a common and inevitable activity in People’s Daily life.Research shows that 36% of adult falls occur on steps,and the accident rate of falling down steps is much higher than that of going up steps.Current research focuses on steps to walk in the gait analysis,general or the difficulty of using steps walking characteristics evaluation exercise in old people walking steps,or the impacts on the stability of multitasking to walk,but these studies only for single joints were analyzed,and ignore the synergy between multiple joints,,walking down the steps of the lower limb power chain on dynamic characteristics and differences,And the mechanics of the higher risk of falling down steps remains unclear.Therefore,the purpose of this study is to analyze the dynamic characteristics of lower extremity multi-joint in the process of stepping up and down of healthy subjects,to explore the dynamic mechanism of falling more easily than that of stepping up and down,and to further analyze the influence of different speeds on the biomechanical characteristics of lower extremity multi-joint in step walking.Methods:In this experiment,13 healthy young female subjects from Shanghai Institute of Physical Education were recruited.The subjects walked up and down steps at three speeds: slow speed,natural speed and fast speed.Vicon 3D infrared motion capture system was used to collect subjects’ kinematics data at a sampling frequency of200 Hz.The self-built experimental step is combined with Kistler 3D force measuring platform to collect the ground reaction force and other dynamic data of the subjects,and the sampling frequency is 1000 Hz.Noraxon Wireless Surface EMG Tester collects surface EMG signals from lower limb muscles of subjects at a sampling frequency of 2000 Hz.Using two-factor variance analysis,compare the steps walking(up/down by three kinds of speed)of lower extremity hip,knee and ankle joint kinematic parameters(joint Angle),the kinetic parameters(the ground reaction force,internal force of joint torque,power and knee joints),and muscle activity(root-mean-square amplitude,activation)differences,significance level is set to alpha = 0.05.Results:1、Up and down the steps of action mode: 1)the stairs: foot touchdown,hip and knee synchronous stretching,joint activities about 55 ° almost unanimously,ankle relatively static,relies mainly on the hip and knee doing positive work to drive the body center of gravity forward,upward into the first pair of support,ankle plantar flexion,doing work off the steps and lower limb power orderly three joints.There was no significant difference in the peak torque of the three joints of lower limbs between the upper and lower steps(P BBB 0 0.05).2)down the steps,rely mainly on large buckling of knee,ankle joint,joint range respectively about(80 °,65 °),the next step is knee ankle joint complex leverage model,ankle as the end of the lower limb kinematic chain have the effect of dynamic support,knee,ankle,and at the same time doing negative work to control the body center of gravity down,lower limb muscles do concession contract.The peak of knee torque during step descent appeared at the end of single support period.2、 Internal force of knee joint: 1)The shearing force of tibial platform on the lower step was higher than that on the upper step at all three speeds,and the shearing force on the lower step was significantly higher than that on the upper step at slow speed and natural speed(1.34±0.43:1.86±0.59;1.32± 0.35:1.92±0.56);2)The tibial plateau pressure,patellofemoral pressure and patellofemoral stress of the lower step were all lower than those of the upper step at different speeds.3、 SEMG signals: 1)Compared with descending steps,the lower limb muscles were more activated in ascending steps,and the root mean square amplitude of hamstring muscles and medial and lateral gastrocnemius muscles in ascending steps was significantly higher than that in descending steps(P < 0.05).When walking up the stairs at different speeds,the degree of muscle activation increased with the increase of the speed,but when walking down the stairs,it did not conform to this rule.2)The knee joint muscle co-activation was significantly higher than that of the down step movement(P < 0.05),and the ankle joint muscle co-activation was significantly lower than that of the down step movement(P <0.05).Conclusions:1、 The action mode of stepping up is the orderly activity of a single lever.The ankle joint performs relatively static support from touching the ground to the single support stage,and the lower limb muscles contract to the heart.The movement mode of descending the steps is the complex lever mode of joint action of knee and ankle.The lower limb motor chain actively seeks for the steps,and the foot touches the ground for dynamic support.The knee and ankle joint do negative work at the same time,and the lower limbs on both sides coordinate the force,and the muscles contract concessively,which greatly increases the control difficulty.The end of the single support at the bottom of the step may be the critical period when falls are most likely to occur.2、 Compared with the upper step,the shearing force of the tibial plateau of the knee joint at the lower step is higher,which may be related to the flexion Angle of the knee joint at the higher lower step.3、The muscle activation degree of the lower step is obviously less than that of the upper step,but the joint torque of the lower step is similar to that of the upper step,and the difficulty of muscle control is increased.In the process of walking up and down steps,the quadriceps muscle was the dominant muscle activation pattern,and the activation degree of quadriceps muscle and hamstring muscle did not match in the process of walking down steps,leading to reduced joint stability,thus increasing the potential risk of falling. |
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