Hamstring Muscle Kinematics During Accelerate Phase And High-speed Phase Of Sprinting

Purpose: Hamstring muscle strain injury is one of the most popular injuries among sports injuries.The current mechanism of the hamstring strain in sprinting process is still controversial at present.The main controversy is about when the strain happens during a gait cycle.Besides the influence of body posture on the hamstring muscle strain injury rate is not determined yet.The purpose of the present study was to compare the difference of the biomechanical characteristic of hamstring muscle between high-speed phase and acceleration phase in sprinting and the relationship between joint angle and muscle strain.Methods: Ten male and ten female athletes major in track events participated in this present study.Straight leg raise test was used to collect the flexibility data of each subjects.Qualisys system and Delsys system were used to collect the kinematic and EMG data.The trunk angle,pelvis angle,hip angle knee angle,muscle length and muscle strain were calculated by Visual 3D.Results: Among female athletes,the length of biceps femoris muscle during high-speed phase was significantly longer than in accelerate phase(p=0.006),but no significant difference was found about the length of semitendinosus muscle and semimembranosus muscle between the two phases among female athletes(p=0.35,p=0.124).Among male athletes the length of the two muscles mentioned above was significantly longer during high-speed phase.In male subjects,the biceps femoris muscle,the semitendinosus muscle and the semimembranosus muscle had a negative correlation with their flexibility in accelerate phase(r=-0.730,p=0.017;r=-0.644,p=0.045;r=-0.698,p=0.025).During the high-speed phase,the flexibility of hamstring muscle has significant negative correlation with maximal strain of the biceps femoris(r=-0.651,p=0.041)in male subjects,but have no significant correlation with maximal strain of the semitendinosus muscle and semimembranosus muscle(r=-0.621,p=0.055;r=-0.631,p=0.050).Conclusion: During accelerate phase,the trunk and pelvis are tilted forward.This state may elongate the hamstring muscle at the starting point.The knee joint is flexion during the whole gait period,which can shorten the hamstring muscle at the end point.During the high-speed phase,the trunk and pelvis angle is smaller than in the accelerate phase and the knee joint angle is also smaller than in the accelerate phase and the knee joint angle is also smaller than in the accelerate phase.The decrease of knee joint angle may be the reason for increasing the length of hamstring.This may also contribute to the hamstring muscle length in high-speed phase is longer than in accelerate phase.During the high-speed phase,the late support period has a higher risk for hamstring muscle strain injury.During accelerate phase,the late swing period have a higher risk.The activation of semitendinosus muscle will increase with the increased speed of sprinting.The lager the range of motion,the higher the average activation of hamstring muscle.Male athletes with better flexibility are at a lower risk of hamstring strain injury during the accelerate phase.