The Effect Of Middle Speed Running At Different Slope On The Biomechanics And Work Mode Of The Three Joints Of Human Lower Limbs

Research purposes:Cross-country running and mountain ultramarathon-related sports events are more challenging and attractive due to the multi-gradient slope changes,high difficulty,and long distance.In recent years,they have become more and more popular with runners.In the daily training of trail running events and mountain runners,adapting to various slopes and their changes is the ability that runners must possess and the challenges they face.A deep understanding of the adaptability of the human body to changes in slope is essential for daily health and competition training.Running slope is an important factor affecting running load.In the special competition training of uphill and downhill running,the human body will bear repeated mechanical load stimulation several times its own body weight.The load on the joints of the lower limbs may change with the steepness of the slope,especially the joint stress and stiffness.Once the load exceeds the load or load intensity that one can bear,the risk of injury will also increase.The degree to which the change of the slope and the steepness of the slope will affect the incidence of running sports injuries remains to be further studied.In training practice,whether or not to optimize the energy output of the three-joint muscles of the lower extremities through intensive training of specific lower extremity joints,and thereby improve the running performance under specific slope conditions,also needs further research.In summary,the purpose of this study is to compare the difference between the biomechanics of the lower limbs,especially the stiffness of the ankle,knee,and hip joints,and the contribution of work to horizontal running when running uphill and downhill at different slopes under moderate speed conditions.Exploring the changes in the stiffness of the lower limbs and the contribution of joint work after the running slope changes,as well as the potential impact on the incidence of sports injuries and the improvement of sports performance.Research method:Using a dynamometer treadmill(1000Hz)and infrared motion capture system(100Hz)to collect 16 healthy male sports enthusiasts at(-9°,-6°,-3°,0°,3°,6°,9°)7 slopes and medium speed(2.78m/s)kinematics and dynamics data during running.Data of 46 landmark points were collected statically,15 seconds of data(complete10 gait cycles)after one minute of running at each slope were dynamically collected,and the support period and sagittal data of the right lower limb were analyzed.Single factor repeated measurement analysis of variance was used to analyze the influence of running slope on time and space parameters,lower limb three joints,center of gravity and torso kinematics,impact force,lower limb three joint dynamics,vertical stiffness,joint stiffness,and contribution to work.Research results:(1)The impact of running at different slopes on time and space parameters is mainly reflected in the increase in step frequency and decrease in step length when running on steeper uphills and downhills.The change of slope has a significant impact on the running support period,the flight period,the step time and the touchdown index(P<0.05).(2)Except for the maximum extension angle of the knee joint,running at different slopes had significant effects on the kinematics of the joints and the center of gravity(P<0.05).First of all,the range of motion of the ankle and hip joints and the angle of the initial touch of the foot are linearly increasing under the measured 7 slopes;the range of motion of the knee joint is distributed in a U-shaped curve,and the angle of the initial touch of the foot is an inverted U-shaped curve.distributed.Secondly,the maximum forward inclination angle of the trunk and the sagittal range of motion in uphill running were significantly increased,and the maximum forward inclination angle and the maximum backward inclination angle of the trunk in downhill running were significantly reduced.Finally,the vertical displacement of the center of gravity is significantly reduced when running steeper uphills and downhills.(3)Different slopes have a significant impact on the results of running impact(P<0.05).The peak impact force and the time of occurrence are linearly decreasing at the 7 measured slopes;the horizontal braking force and the propulsion peak are only symmetrically distributed during horizontal running;the braking and propulsion periods are only symmetrically distributed during shallower uphill slopes.(4)Running at different slopes has a significant impact on joint dynamics(P<0.05).The net mechanical work on all slopes is positive for the ankle joint and negative for the knee joint;the net mechanical work of the hip joint is positive for all uphill runs,and negative for horizontal and downhill runs.(5)Different slopes have significant effects on the results of running stiffness(P<0.05).The vertical stiffness presents a U-shaped curve distribution on the 7measured slopes,and the vertical stiffness of steep slope running is significantly increased;compared with the horizontal slope,the ankle stiffness of the 9°downhill running is approximately doubled(0.87vs1.74),the stiffness of the knee joint increased about 2 times(2.11vs6.14),and the stiffness of the hip joint increased about 5 times(1.17vs5.57).(6)Different slopes have significant effects on the work pattern of running joints(P<0.05).When running horizontally,the contribution of ankle joint work accounted for 53%;knee joint accounted for 31%;hip joint accounted for 17%.When running 9° uphill,the contribution of ankle joint work accounted for 25%;knee joint accounted for 17%;hip joint accounted for 58%.When running 9° downhill,the contribution of ankle joint work accounted for 9%;knee joint accounted for 55%;hip joint accounted for 36%.Research conclusions:(1)Compared with horizontal running,running kinematics and dynamics parameters change significantly after reaching a certain uphill or downhill slope.(2)The vertical stiffness increases significantly when the slope is steeper uphill and downhill.The stiffness of the joints increases significantly when running downhill,especially the knee joints,followed by the hip joints.It indicates that there is a greater risk of knee and hip injuries when running downhill.Common running sports injuries such as patella-femoral syndrome and iliotibial band syndrome are related to these two joints.(3)The influence of running at different slopes on the work pattern of joints is reflected in the evolution from the ankle joint dominance when running horizontally,to the hip joint dominance when the slope is steep and the knee joint when the slope is steep downhill.Functional movement training for specific joints or attention to the movement patterns of specific joints during slope running training may be of great significance to improving the performance of slope running.