The Impact Of Shank Mass And Inertia Manipulation On Sprint Kinematics And Kinetics

Objective:Setting sprinting as the target movement, discussed the effects of different shank mass(0%, 10% and 15% shank mass loadings) on lower limb kinetics and kinematics during the course of sprinting,(1) discussed the effects of different shank mass(shank loadings) on spatial temporal parameters and sprinting performance.(2) compared the lower limb kinematics data(angles and range of motion of hip, knee and ankle) with different shank mass, to quantize the effects of this training method on sprinters’ sprinting techniques during the course of sprinting.(3) analyzed the effects of this training method on sprinters’ lower limb kinetics data using joint torque, joint power and joint energy contribution. Therefore, explored the effects of this training method on sprinters’ biomechanics data during the course of sprinting, discovered the mechanism of this training on developing sprinters’ specific strength, tried to provide theoretical and practical help to improve training method and sprinting performance.Methods:12 male college students specialized at sprinting from Shanghai University of Sport and 6 male sprinters from Tsinghua University were selected. The 3 dimensional data collecting environment was built on the sprinting track in the Shanghai University of Sport stadium. The start line was set 40 m far away from the first force platform, subjects were required to sprint through the data collecting environment with 3 different shank loadings(0%, 10%, 15% of shank mass). Using VICON and Kistler force platforms to collect the lower limb kinematics and kinetics data synchronously, using Visual 3D to conduct the data process and compute the spatial temporal data(including step length, step frequency, flight time, stance time, stride time, average speed of the COM), kinematics data(including peak degree of left hip, knee and ankle), kinetics data(including left hip, knee and ankle joint torque at the left foot touch down time and toe-off time, the peak value of left hip, knee and ankle joint torque, peak value of left hip, knee, ankle power, the joint energy contribution of left hip, knee and ankle during stance phase and swing phase).Results:(1)The average speed of COM has decreased significantly with the increase of the loading mass. The step length and step frequency decreased significantly when the loading mass came to 10% of shank mass. Besides, the stance time increased significantly when the loading mass came to 15% of shank mass.(2) The peak hip flexion degree dropped significantly as a result of the increase of loading mass. Meanwhile, the peak ankle plantar flexion degree dropped significantly when the loading mass came to 15% of shank mass. As for the range of motion(ROM), the ROM of hip decreased significantly when the loading mass came to 10% and 15% of shank mass. The ROM of ankle decreased significantly when the loading mass came to 10% of shank mass.(3) The ankle torque at the touch down(TD) moment and the hip torque at the toe-off(TO) moment dropped significantly when the loading mass increased. In addition, the 2nd peak value of the knee extension torque dropped significantly when the loading mass increased. As for the joint power, the peak hip power dropped significantly when the loading mass came to 15% of shank mass, peak ankle power dropped significantly when the loading mass increased from 10% to 15% of the shank mass.(4) During the stance phase, the joint absorbed energy contribution of hip decreased as well as the joint generated energy contribution of ankle increased when the loading mass increased. During swing phase, the joint generated energy contribution of hip and knee has changed significantly, the joint generated energy contribution of hip decreased as well as it of knee increased when the loading mass increased.Conclusion:The ROM of hip and ankle decreased during the course of sprint as a result of the increase of shank mass, the result pointed out that this training method might induce the change of sprinters’ sprinting techniques. The joint torque and power of hip, knee and ankle dropped when the loading mass came to 15% of shank mass, however, the knee torque at the TO moment increased significantly. Besides, the knee absorbed more energy during stance phase as well as the knee generated more energy during swing phase. These results were connected with the location of the loadings, different loading location will lead to different changes of joint torque and power, therefore brings different training results.