Influence Of Landing Height On Knee Biomechanics Characteristics During Single Leg Drop Jump

Objective:The aim of this study is to analyze the biomechanical characteristics of knee during single leg drop jump at different drop heights.By analyzing the biomechanical characteristics,we expect to find out the potential risk factors of knee injury.It is helpful to provide basis for athletes to choose the most suitable height to develop their lower limb power.At the same time,according to the gender differences in the biomechanical characteristics,we can design training programs respectively based on gender difference.It is of great significance to athletes’ scientific training.Methods:In this study,20 volleyball players were selected.They were asked to jump off three boxes.The boxes were of 15cm(DJ15),30cm(DJ30)and 45cm(DJ45)height.Subject fell from the box with no initial speed and with hands akimbo.They should land on dominant legs.After landing they must try their best to take off vertically as soon as possible and then fell back to the ground with body balanced.We uesd 3D infrared motion capture system,3D force measuring platform and surface EMG to synchronously record the 3D whole-body kinematics signals,ground reaction force signals and surface EMG signals.Qualisys Track Manager 2019.2data acquisition system software was used to identify the Markers.Visual 3D software was used to process and calculate the relevant targets.Kinematics,kinetics and EMG signals during drop jump were analyzed by variance characteristics.The influence of landing height and gender were analyzed comprehensively.The targets included knee angle,torque,shear force,power,muscle activation.Results:(1)The maximum knee flexion Angle was significantly increased with the increase of height(P < 0.05),and the maximum knee valgus and external rotation angles of man were significantly lower than those of woman in both braking period and take off period(P < 0.05).The range of knee flexion of man was significantly lower than that of woman(P < 0.05).(2)The maximum rotation shear force and the maximum forward shear force of knee during braking period were significantly increased with the increase of height(P < 0.05).(3)The knee flexion moment in the braking period was significantly increased with the increase of height(P < 0.05).The knee flexion moment in the braking period and the take off period was significantly greater in men than in women(P < 0.05),and the knee valgus moment in the braking period and the take off period was significantly greater in women than in men(P< 0.05).(4)The knee valgus power of man was significantly lower than that of woman during braking period(P < 0.05).The flexion power and internal rotation power of the knee in the take off period were significantly increased with the increase of height(P < 0.05),and the varus power of the knee in man was significantly lower than that in woman(P < 0.05).(5)The RMS amplitudes of vastus lateralis,rectus femoris,vastus medialis,semitendinosus,biceps femoris,lateral gastrocnemius and medial gastrocnemius increased significantly with the increase of height(P < 0.05).The RMS amplitudes of vastus medialis in the braking period were significantly lower in men than in women(P < 0.05).and the RMS amplitude of the medial gastrocnemius in man was significantly higher than that in woman(P< 0.05).(6)There was no significant difference in the co-contribution rate of thigh(P > 0.05),and there was no significant difference between genders(P > 0.05).Conclusion:(1)Kinematic characteristics of single leg drop jump at different heights were as follows:the maximum knee flexion angle increased with the increase of landing height.Women showed significant knee valgus and external rotation in order to maintain joint stability.(2)Kinetic characteristics of single leg drop jump at different heights were as follows: the extension power of knee increased with the increase of landing height.In the braking period,the sagittal plane and frontal plane of man and woman showed significant differences: knee flexion moment and flexion power were significantly greater in man than in woman,while knee valgus moment and valgus power were significantly greater in woman than in man.(3)The characteristics of muscle activation of single leg drop jump at different heights were as follows: landing height significantly affected the activation of knee muscles during braking period,but had little effect on the take off period.There was significant gender differences in neuromuscular control strategies,the medial vastus muscle activation was significant in women during braking period and the medial gastrocnemius muscle activation was significant in men during pedaling period.