Acute Effects Of Hamstring Stretching On Jump Height And Knee Loading In Females During A Stop Jump Task

Objective: The purpose of this paper is to determine the acute effects of hamstring static stretching on jump height and impact on the anterior cruciate ligament injury risk in females during a stop jump task by measuring the center of gravity height, knee kinematics, knee dynamics and other parameters. Methods: Twelve female martial players completed two tests in discontinuous two days: 1) no stretching + stop jump 2) hamstring static stretching + stop jump. A Vicon system, two Kistler forceplates and Delsys surface EMG acquisition system were synchronously used to collect the subjects of lower extremity motion trajectory, ground reaction force and EMG data during a stop jump landing in two different ways of warm-up. Using Visual 3D analysis software to calculate the lower extremity kinetics, kinematics, the paired T-test was applied to compare the difference between no stretching and hamstring static stretching routine on stop jump kinematics, dynamics and EMG data. Results: Compared to the no stretching, there were significant increases in the jumping center of gravity height for the hamstring static stretching, increased 4.8%(P<0.05). A significantly increased was found on the maximum speed of the knee extensor when comparing no stretching with hamstring static stretching(P<0.05), but no significant difference was found for maximum valgus torque and the anterior tibia shear force(P>0.05). Analysis also revealed biceps femoris EMG decreased significantly in the flexion process(AEMG-1) after hamstring static stretching(P<0.05). Conclusions: After hamstring static stretching, the height of stop jump did not decline, and the main reason is that after hamstring static stretching, the maximum speed of the knee extensor increased significantly, thereby improving the jump performance. There is not increase the knee loading and not increase the risk of anterior cruciate ligament injury after hamstring static stretching. Current evidence suggests that performing hamstring static stretching is a viable and safer way to warm-up, will not have a negative impact on performance.