Pre-activation Characteristics Of Lower Limbs In Volleyball Players With Different Relative Heights Of Drop Jumps

Purpose: The aim of this study was to analyze the trends of lower limb muscle preactivation characteristics in volleyball players during drop jumps of different relative heights and the gender differences in lower limb muscle pre-activation characteristics during drop jumps of the same relative height.By analyzing the influence of relative height and gender factors on the pre-activation characteristics of lower limb muscles during the drop jump,the neuromuscular control mechanism of the pre-activation phase of the drop jump can be explored,which can help to improve the scientific level of drop jump training methods.Methods: 20 high-level volleyball players(17 national athletes and 3 national level athletes)were the experimental subjects,including 9 males and 11 females.The drop jump test was done at 50%,75%,100% and 125% of the maximum vertical jump height(MVJH),respectively.Two 3-D force tables(Kistler 9281 EA,Winterthur,Switzerland)were used to record ground reaction force and time to touchdown.A Delsys Trigno Lab16-channel wireless surface electromyograph(Delsys,Boston,MA,USA)was used to acquire EMG signals from the quadriceps(rectus femoris,lateral femoris,medial femoris),hamstrings(semitendinosus,long head of biceps femoris),triceps surae(medial and lateral heads of gastrocnemius,soleus),and anterior tibialis muscles 150 ms before foot touchdown.The 3D dynamometer signals were synchronized with the surface EMG signals using a wireless surface EMG synchronization trigger(Delsys,USA).Two-way repeated measures(ANOVA)were used to analyze the standardized root mean square amplitude of lower limb muscles and the co-activation ratio of knee and ankle muscles during the pre-activation phase of the drop jump movement using different relative drop heights(50%,70%,100% and 125% MVJH)and gender(male and female)as factors.Results:(1)With the increase of drop height,the level of pre-activation of lateral femoral and triceps surae muscles in male athletes as well as anterior tibialis and medial head of gastrocnemius muscles in female athletes increased significantly(P < 0.05).(2)There was no significant difference in the pre-activation levels of knee muscle groups between male and female athletes from 50% to 100% MVJH(P > 0.05),while the pre-ctivation levels of quadriceps pre-activation levels and knee joint co-activation ratio were significantly greater in male athletes than in female athletes at 125% MVJH,and the pre-activation levels of semitendinosus and triceps surae muscles were significantly greater in female athletes than in male athletes(P < 0.05).Conclusions:(1)The height of drop jump significantly affected the pre-activation level of lower limb muscles,which was mainly influenced by the autonomic regulation of central nervous system to adapt to the impact load at different heights when the height changed.(2)The drop height significantly influenced the gender differences in lower limb preactivation,with 100% MVJH as the threshold.The gender differences in knee muscle pre-activation levels were not significant below 100% MVJH,and above 100% MVJH male athletes preferred active knee muscle force control over female athletes,while female athletes preferred active ankle muscle force control.