Research Of Resistance Sled Sprint With Different Loads On The Biomechanical Characteristics Of The Lower Limbs

Purpose:This study measures the kinematic and kinetic parameters of soccer players during the resistance sled sprint（RSS）,analyzes the relationship between external load and rate of sprint velocity decrease(%V_dec),observe the kinetic and kinematic characteristics with different loads of RSS on soccer players and discusses the optimal load for RSS.Methods:The experiment was divided into two parts.Part 1:29 college football players（except goalkeepers）from Beijing Sports University.and let them randomly perform 5 times RSS training in no weight,13%body Mass（BM）,15%BM,20%BM and 25%BM on the artificial grass.The sprint distance is 20m,and the athletes must rest at least 5min after each sprint.Use body composition meter,infrared velocimeter and other equipment to measure subject body composition and 20m sprint speed index.Pearson correlation and linear regression were used to analyze the relationship between external load（%BM）and%V_dec,and A one-way analysis of variance（ANOVA）with repeated measures were use to analyze the sprint performance under 5 kinds of load bearing intervention conditions.Part 2:Recruit 13 college football players（except goalkeepers）from Beijing Sport University,and let them randomly perform 5 times RSS training in no weight,10%V_dec,15%V_dec,20%V_dec,and 25%V_dec on the artificial grass.The sprint distance is 20m,and the athletes must rest at least 5min after each sprint.The first-step mechanical characteristics were collected by Force plate,the angles of joint of trunk and lower limbs were collected by High-speed infrared camera and the sprint time were collected by Infrared speedometer.The change characteristics of kinematics and kinetic parameters under 5 kinds of load bearing intervention were analyzed by A one-way analysis of variance（ANOVA）with repeated measuresResults:（1）The linear relationship between the external load（%BM）and the maximum velocity decrease was obtained by regression analysis:%Body mass=1.222×%V_dec+5.8（R²=0.612）;（2）With the increase of the load,the football player’s step length,sprint speed and torso forward angle were significantly reduced when he carried out 20m RSS training（P<0.05）,his ground contact time,propulsion time,vertical impulse,and ankle dorsiflexion angle were significantly improved（P<0.05）,and the impulse was significantly increased at 10%V_dec（P<0.05）.Conclusions:（1）When a football player performs 20m RSS on the artificial grass,there is a high positive correlation between the external load（%BM）and the maximum velocity decrease（P<0.001;r=0.783）.The regression equation is:%Body mass=1.222×%V_dec+5.8（R²=0.612）.（2）The external load can make the ankle dorsiflexion angle increase and the trunk lean forward during RSS.This is helpful for the athletes to force forward more horizontally.（3）During the 20m resistance sled sprint in soccer player,the stride length,the motion Angle of hip and knee joints did not significantly change,and meanwhile the horizontal pushing and stretching force was improved.Recommendation:soccer players should use an external load of no more than 10%V_dec when performing RSS training.