The Investigation On The Relationship Between Leg Muscle Qualities,stiffness And Change Of Direction Ability,and Influencing Factors Of Change Of Direction In Badminton Players

Objective:Change of direction（COD）ability is a key predictor of athletic performance in badminton players,but there are few studies and the correlation between leg muscle qualities,stiffness and COD ability is unclear.In addition,it has been shown that dynamic weight-bearing vest warm-up can significantly improve COD performance of badminton players,but the duration and mechanism of COD performance improvement after warm-up is still unclear,and the reason for improvement is mostly explained by the adaptation of physiological mechanisms.In addition,it has been suggested that the acute change in lower limb stiffness may also be one of the macroscopic mechanisms of COD performance enhancement in athletes,but whether the acute increase in lower limb stiffness after warm-up is an influencing factor of COD performance enhancement remains to be directly investigated.Therefore,this study first investigated the relationship between leg muscle qualities and stiffness and COD capacity of badminton players through a cross-sectional study.In addition,a longitudinal study was conducted to investigate whether the increase in COD performance of badminton players after warming up with dynamic weight-bearing vest was due to the acute increase in lower limb stiffness and the duration of the change to provide theoretical support for coaches and athletes to conduct badminton training more scientifically and then improve sports performance.Methods:This study included a cross-sectional study（Study I）and a longitudinal study（Study II）.Study I included a total of 45 active badminton players（22 males and 23females）from a provincial team.Before warm-up,the athletes were measured with Myoton PRO（Myoton PRO,Myoton AS,Tallinn,Estonia）for individual muscle and tendon stiffness（standing position）,including the rectus femoris（RF）,soleus,and medial gastrocnemius（Med Gast）,Achilles’tendon（AT）and patellar tendon（PT）were included in 10 muscles and tendons.After the test,the athletes performed badminton player’s routine warm-up procedures followed by badminton COD test,maximum isometric muscle strength test and vertical stiffness(K_vert)test(including left and right-side single leg and double leg K_vert)in sequence.A total of 15（9 males and 6females）varsity athletes and first-class athletes from Shanghai Sports Institute were included in Study 2.Individual muscle and tendon stiffness tests,K_vert(including left and right single and double leg K_vert)and COD tests were performed on athletes in a standing position prior to warm-up with dynamic weight-bearing vest.The athletes repeated the pre-warm-up（T0）series of tests sequentially from 0-6 min（T6）,7-12 min（T12）and 13-18 min（T18）after the dynamic weight vest warm-up（weight 10%of their body weight）.Study 1 used Pearson correlation analysis to investigate the relationship between leg muscle qualities and stiffness indexes and COD performance;Study 2 used one-way repeated measures ANOVA to compare the changes in athletes’COD performance and lower limb stiffness before and after warm-up,and used covariance analysis to analyze the effect of lower limb stiffness on athletes’COD performance.Results:The results of experiment 1 showed that 1)quadriceps muscle imbalance and COD performance were highly negatively correlated in national excellent female athletes（P=0.01）;2)PT stiffness in the right leg was highly positively correlated with COD performance in national excellent male athletes（P=0.04）;and bilateral lower limb AT（left:P=0.001;right:P=0.03）and PT stiffness in first-class male athletes（left:P=0.04;right:P=0.02）were both highly negatively correlated with COD performance;overall K_vertwas highly positively correlated with COD performance in national excellent female athletes（P=0.006）;and right leg K_vertwas highly positively correlated with COD performance in all first-class female athletes（P=0.03）.The results of Study 2showed that there was a significant interaction effect in time for athletes’COD performance at T6,T12 and T18 compared to T0（F=13.948,P<0.001,η_p²=0.499）.Bonferroni post hoc test showed that T6（P=0.018）,T12（P=0.010）and T18（P=0.004）T6,T12 and T18 showed a significant increase in right leg AT stiffness compared to T0（F=3.103,P=0.046,η_p²=0.181）.Based on the analysis of covariance,it was concluded that the right leg AT stiffness of the athletes（F=3.573,P=0.081,η_p²=0.216）had an effect on the COD performance.Compared to T0,PT stiffness of the right leg measured at T6 was significantly lower（F=4.713,P=0.048,η_p²=0.252）.Based on the analysis of covariance,it was concluded that the right leg PT stiffness of the athletes（F=2.327,P=0.151,η_p²=0.152）had an effect on the COD performance.Compared to T0,T18 measured a significant increase in right leg AT stiffness（F=6.383,P=0.024,η_p²=0.313）.The Soleus stiffness of the left leg measured at T12 was significantly increased compared to T6（F=4.739,P=0.047,η_p²=0.253）.Based on the analysis of covariance,it was concluded that the athletes’left leg Soleus（F=0.415,P=0.531,η_p²=0.031）had an effect on COD performance.Compared to T6,T18 measured a significant increase in right leg AT stiffness（F=5.207,P=0.039,η_p²=0.271）.Med Gast stiffness of the right leg measured at T18 was significantly increased compared to T12（F=4.652,P=0.049,η_p²=0.249）;according to the analysis of covariance,Med Gast stiffness of the athlete’s right leg（F=8.540,P=0.012,η_p²=0.396）had no effect on COD performance.k_vertand RF stiffness did not undergo any significant changes both before and after the warm-up.Conclusions:Study I concluded that 1)in terms of leg muscle qualities of badminton players,quadriceps muscle strength imbalance in national excellent female athletes was associated with change of direction ability.2)in terms of lower limb stiffness characteristics of badminton players,lower limb Achilles and patellar tendon stiffness in male athletes and lower limb vertical stiffness in female athletes were associated with change of direction ability.Study 2 concluded that the increase in the stiffness of the right leg Achilles tendon and the left leg soleus muscle of the athletes after the warm-up of the dynamic weight-bearing vest and the decrease in the stiffness of the patellar tendon of the right leg may be one of the macroscopic mechanisms leading to the enhancement of the change of direction ability after the warm-up of the dynamic weight-bearing vest in badminton players,and the duration can be up to 18 minutes.