Biomechanics Of Maximum Velocity Phase Of Sprinting With Additional Mass On Shanks

Purpose: Additional mass load-running is a kind of popular training method employed by athletes to develop special strength and improve sprint performance,but the mechanism and scientific basis of this training method have not been clear,and only a few studies kinematically were evaluated whether this training methods will impact on the athletes technology.The purpose of this study is: to bond additional mass on shanks in two different positions as the basic experimental protocol,to collect the data of maximum velocity phase of sprinting with a giving mass(0.8%subjects body weight),and to study the effects of lower limb inertial parameters(mass and moment of inertia)changes on ground reaction force,kinematics and three joint muscle torque of lower limb,and the scientific basis of this method.The specific aims are included:(1)to study the changes of lower limb kinematics with respect to0-weighted running in one gait cycle during load-running in two load positions;(2)to calculate the three joint muscle torque of lower limb with intersegment dynamics,and to compare the changes of the lower limb dynamics of load-running relative to those of 0-weighted running;(3)to discuss the biomechanical effects of load position and load mass on load-running,and to improve the training method;(4)to discuss the biomechanical mechanism of the training method of load-running for the development of joint muscle strength,and to provide theoretical guidance for training practice.Method: In this study,8 second-class sprint athletes were selected as the subjects,and the loads of 0.8% respective body weight were added to both sides of the shanks,under the knees and above the ankles,respectively.The 0-weighted running,the under-knee-load-running and above-ankle-load-running were performed in random order,and the high-speed images and the ground reaction force data were acquired synchronously during the gait cycle.The basic spatiotemporal parameters,kinematics parameters and dynamics parameters of three running states were calculated.The dynamics parameters included the ground reaction force and the intersegment moment between the three joints of the ankle,knee and hip.Results:(1)Compared with the 0-weighted running,there were some changes in the load-running spatiotemporal parameters: additional mass reduced the running speed and running length,and increased stance-phase time,swing-phase time,the relative angular velocity of both thighs.Overall,the load of additional mass reduced the performance of running in both load-running.(2)Most of the parameters of flexion and extension of load-running had no significant difference with those of 0-weighted running.But the motion ranges of three joints of above-ankle-load-running were less than those of 0-weighted-running;and in under-knee-load-running,the motion range of hip decreased,knee equal,and ankle increased slightly.(3)Compared with0-weighted running,the braking time was shorter and propulsion time was longer,and there were greater horizontal impulse and net horizontal impulse in load-running.(4)The muscle torque peaks of three joints were higher than that of under-knee-load-running and above-ankle-load-running in the whole gait cycle.But the ankle muscle peak value during the stance phase was higher than that of the0-weighted running.Conclusion:(1)The additional mass on the shanks will result in the decrease of running performance and the influence on the movement structure.Closer the load position to the distal,more effect on the performance.(2)Applying proper mass and position of loads for running training,it is not contrary to the principle of "the same movement,the same exercise procedure,slightly increase weight".(3)Compared with0-weighted running,above-ankle-load-running has a longer propulsion duration,promote greater propulsion horizontal impulse and net horizontal impulse,the load-running have a longer working time and the potential for greater muscle strength in the muscles of the concentric contraction stage.(4)Above-ankle-load-running in this study results in greater knee peak torque during the middle propulsion period than those of 0-weighted running.Training in this condition,there will be more potential benefit in concentric contraction of knee extensors than those of 0-weighted running.