The Study Of Lower Extremity Muscle Working Feature And The Risk Of Hamstring Muscle Strain Injury During Sprint Running

Research objectives:To work out lower-limb joints'muscle torque, inertial torque, contact torque and gravitational torque by using the method of intersegmental dynamics, and to quantify every joint's angular variation and lower-limb muscles' power, so as to promote the understanding of lower-limb joints dynamics in sprint running; To quantify lower-limb single muscle's length and speed variations in sprint running, and to study the objective function and arithmetic of optimization that reflect human body's optimal control of neuromuscular system in sprint running; To estimate muscle stress by using the method of static optimization, thus to further quantify every single muscle's unit power and power sum; To study the damage mechanism and time phase of easily-strained hamstring by analyzing every lower-limb muscle's working feature in the integral gait of sprint running, especially hamstring's working state and its role in sprint running.Research methods:Eight excellent sprinters'two-dimensional kinetic data (300 Hz) and the data of the ground's counterforce (1200Hz) are collected in integral gait in their maximum velocity sprint running on a synthetic surface track. In addition, this research applies the approach of intersegmental dynamics to analyze the torque of every lower-limb joint, and to work out the variations of joints angle and muscles power. Based on every examinee's lower-limb skeletal morphological parameter and his two-dimensional kinetic parameter in sprint running, this research tries to work out respectively length and speed variations of lower-limb major muscles and tension arm variation of every joint by utilizing the method of computer analyzing system of the muscular function model of human lower extremity. In addition, this research also builds a two-dimensional lower-limb musculoskeletal model, establishes objective function and constraint equation, and applies mesoscale sequential quadratic programming pseudo-newton for linear search algorithm to optimize muscle's torque, thereby working out single muscle's stress, and further works out muscle unit power and its total power.Research results:During the support phase it is muscle torque and contact torque that take control, and the main function of muscle torque is to withstand contact torque. Meanwhile the peak value of angular velocity and that of the extensor muscle's positive power emerge in turn from proximal end to distal end. During that phase the ankle's peak values of angular velocity and muscle power are obviously higher than those of other joints, while the power of knee muscles is much lower than that of hip and ankle muscles. During the swing phase the main joint torques are muscle torque and inertial torque, and muscle torque controls action by acting negatively on inertial torque. In the complete gait of sprint running the peak values of the powers of hip extensor muscles, knee flexor muscles and ankle plantar flexion muscles are apparently higher than those of hip flexor muscles, knee extensor muscles and ankle dorsiflexion muscles. And in the mean time when hip extensor muscles and knee flexor muscles are doing positive work, their peak values of powers are evidently higher than the time when they are doing negative work, and when ankle plantar flexion muscles are doing negative work its peak value of power is obviously higher than the time when they are doing positive work. During every phase the stress value of such two-joint muscles as HAM, RF and GAS is higher than that of the other muscles that do work, and in the integral gait their peak value of stress and the negative work they accumulate in a single gait(the per unit negative work in a single gait) are higher than those of the other muscles. As a kind of antagonistic muscle, every muscle, to some extend, fights against contact torque and inertial torque when it contracts eccentrically and does negative work. In sprint running, some joint muscles do positive work and negative work to two joints at the same time. In the middle phase of swing, hamstring will be triggered abruptly in its compliance eccentric contraction and its peak value of power of negative work emerges immediately. In the telophase of swing peak values of hamstring's length, speed and stress appears. At the moment of touching the ground hamstring's stress and per unit power increase quickly to the peak values in support phase, and the peak values of biceps femoris'stress, length and power of doing negative work and sum of negative work are obviously higher than those of semimembranosus and semitendinosusResearch conclusions:In sprint running, external and inertia forces acting on joints of human body (including Coriolis force and centrifugal force) greatly influence the working nature of joint muscles. In the support phase, an outstanding runner can successfully transfer energy to ankle joints, that is, from proximal end to remote end, which strengthens its power on the ground, thus to keep his running speed in a better way. The main function of knee joints is to keep the height of gravity center and deliver energy from hip joint to ankle joint. In sprint running, it is very important of the active swift contractility of hip extensor muscles and knee flexor muscles, and of ankle plantar flexion muscles'passive swift contractility. For that reason, in the specialized training of sprint running, great importance should be attached to lower-limb muscles' ability of doing work under the circumstances of eccentric contraction. Meanwhile, trainers should try to find out a new training method that is similar to the complicated working feature of lower-limb muscles in sprint running. The research also finds out that lower-limb two-joint muscles are most easily strained in sprint running, that in sprint running hamstring is easily strained in the middle phase and telophase of swing and at the moment of touching the ground, and that long head of biceps femoris muscle is the most easily strained muscle in hamstring muscles.