Reliability And Correlation Analysis Of Dynamic Strength Index And Force-Velocity Imbalance

Background:Maximum strength and explosive power are two of the most important factors affecting athletic performance.More and more attention has been paid to the accurate testing and evaluation of athletes’ maximum strength and explosive power.The Isometric Mid-thigh Pull and Countermovement Jump are often used to test athletes’ maximum strength and explosive power.At the same time,the Dynamic Strength Index and Impulse-based Dynamic Strength Index obtained by comparing the peak force and impulse of Countermovement Jump and Isometric Mid-thigh Pull,as well as the ForceVelocity Imbalance obtained by Countermovement Jump test with different loads have been widely paid attention to in evaluating the strength quality of athletes and guiding sports training.However,there are still some gaps in existing studies on the reliability and their correlation of the above three indicators.Based on this,the purpose of this study is to verify the retest reliability of Dynamic Strength Index,Impulse-based Dynamic Strength Index and Force-Velocity Imbalance.At the same time,explore the correlation between Dynamic Strength Index,Impulse-based Dynamic Strength Index and Force-Velocity Imbalance for evaluating the strength quality of athletes.Methods:Eighteen college athletes with more than 2 years of systematic training experience were selected.The subjects underwent Countermovement Jump and Isometric Midthigh Pull tests on two days respectively,in which the Countermovement Jump carried three loads: no weight,30% body weight and 60% body weight.Dynamic Strength Index was calculated by comparing the peak force of Countermovement Jump and Isometric Mid-thigh Pull.By comparing the centripetal impulse of the Countermovement Jump with Isometric Mid-thigh Pull(the time is taken as Countermovement Jump centripetal time),Impulse-based Dynamic Strength Index is calculated.The average force and average velocity of the subjects in Countermovement Jump tests with different loads were used for linear regression to obtain the slope of the force velocity curve,which was compared with the optimal force velocity curve of the subjects to obtain the Force-Velocity Imbalance.Results:(1)Dynamic Strength Index shows good intra-class correlation(ICC= 0.891)and low variability(CV=7.4%).(2)Impulse-based Dynamic Strength Index has a good intra-class correlation(ICC=0.833),but has high variability(CV=19.6%).(3)Force-velocity imbalance shows nearly perfect intra-class correlation(ICC=0.943)and low variability(CV=8.7%).(4)The correlation between Peak force-based Dynamic Strength index and Impulse-based dynamic Strength index is 0.522.(5)The correlation between Force-velocity imbalance and Impulse-based Dynamic Strength Index is-0.499 and the correlation between Force-velocity imbalance and Peak force-based Dynamic Strength Index is-0.388.Conclusion:(1)Peak force-based Dynamic Strength Index and Force Velocity Imbalance have good reliability;Impulse-based Dynamic Strength Index has great variability and does not have acceptable reliability.(2)Peak force-based Dynamic Strength Index has a significant high correlation with Impulse-based Dynamic Strength Index;There is a significant negative correlation between Impulse-based Dynamic Strength Index and Force Velocity Imbalance;There is a negative correlation between Peak force-based Dynamic Strength Index and Force Velocity Imbalance.