Effects Of Different Stiffness Insoles On Lower Limb Biomechanical Characteristics During Long-time Running

Background:With the increasing number of fitness people,especially the rise of marathon running in the folk,people's choice of running shoes is becoming more scientific and functional.Bending stiffness,as a characteristic of shoe midsole,refers to the moment required to bend the unit corner of the forefoot at the metatarsophalangeal joint.Studies have shown that the bending stiffness of the forefoot directly affects the performance of various sports such as running,jumping,sprinting and multi-directional sports,and prevents metatarsophalangeal joint by restricting the metatarsophalangeal joint overstretching.However,there are few studies on the effect of bending stiffness on long-time running.Objective:The purpose of this study is to explore the effect of changing the overall bending stiffness of running shoes on the biomechanical characteristics of the lower extremities during long-term running after replacing running shoes with different bending stiffness EVA insoles,providing a theoretical basis for the design and development of sports shoes,and running Enthusiasts choose appropriate stiffness to provide more targeted suggestions and references.Methods:Customize four kinds of sports shoe insoles with different bending stiffness,which are divided into low stiffness,medium stiffness,higher stiffness and high stiffness insole.Twelve running enthusiasts who meet the conditions were selected,and the experiment order of four pairs of insoles with different stiffnesses was determined by random drawing of the subjects.The four experiments were separated by one week.Each time the experiment is performed for a specific speed of 5 minutes after warming up,the treadmill accelerates to the optional speed,and the treadmill continues to run until the predetermined time is reached.At the end of 10 minutes and long-distance running,the Vicon three-dimensional motion capture system and Bertec force treadmill and other equipment were used to collect kinematics,dynamics,RPE scores and heart rate data.After all four experiments were completed,the two-factor repeated measurement analysis of variance statistical method was used to compare the effects of time and different stiffness on the biomechanical indexes of lower extremities.Results:In the biomechanical test of long-time running,the maximum stiffness of low stiffness insoles before running is greater than medium stiffness(P=0.018),higher stiffness(P=0.011)and high stiffness(P=0.016).The energy loss of the metatarsophalangeal joint of the mid-stiffness insole was lower than that of the low-stiffness group(P = 0.029)and the high-stiffness group(P=0.022),but the energy production of the ankle and hip joints increased.The positive stiffness of the knee joint after running was significantly higher in the low stiffness group than in the higher group(P=0.012)and the high stiffness group(P=0.043).Metatarsophalangeal joint sagittal moment,maximum positive power,maximum angle of dorsiflexion,ankle dorsiflexion moment,valgus moment,flexion and extension activity,valgus activity,maximum dorsiflexion angle,knee valgus activity,maximum flexion Angles,hip internal and external rotation activities and other parameters have statistically significant differences in time factors,after running is greater than before running(P<0.05),after running the ankle joint ground contact angle is higher in the stiffness group than in the medium stiffness group(P=0.005),The metatarsophalangeal joint mobility before running is higher in stiffness than low stiffness(P<0.001)and medium stiffness group(P=0.01),higher stiffness group after running is less than low stiffness group(P=0.014)and high stiffness group(P=0.039).The maximum dorsiflexion angle of the metatarsophalangeal joint before running was lower in the higher stiffness group than in the low stiffness group(P<0.001)and the moderate stiffness group(P=0.023).There are statistical differences in the time factors of ankle joint's ground-off angular velocity,maximum dorsiflexion angular velocity,maximum angular velocity of knee extension,and maximum angular velocity of hip flexion,before running is greater than after running(P<0.05).The bending stiffness of running shoes is significant for the difference between the maximum dorsiflexion of the metatarsophalangeal joint,the maximum angle of the metatarsal flexion,the maximum angular velocity of the dorsiflexion and the maximum negative power of the ankle joint,the angle of the ground,the maximum angle of dorsiflexion,the maximum angular velocity of the dorsiflexion and the metatarsoflexion(P <0.05),the bending stiffness also has a significant difference in the maximum knee extension torque and abduction torque of the knee joint,and there is no significant difference in the hip joint.Conclusions:(1)The bending stiffness of running shoes mainly affects the kinematics of the metatarsophalangeal joint and ankle joint;(2)For running enthusiasts,there is an optimal stiffness for energy saving between medium stiffness and higher stiffness;(3)Higher bending stiffness of running shoes can protect the metatarsophalangeal joint by limiting the dorsiflexion and mobility of the metatarsophalangeal joint;(4)The bending stiffness of higher running shoes plays a shock-absorbing effect by increasing the ground contact angle of the ankle,and the higher stiffness has the smallest ankle valgus angle before and after running,while the low stiffness valgus angle is the largest;(5)Low stiffness running shoes have a higher driving force,but relying too much on the knee joint to work may present a risk of injury.