Kinematic Release Indicators to Four Types of Throw-ins for Junior Soccer Players: A Cross-Sectional Study

The kinematics of soccer throw-in skills has gained increased attention, but the Kinematic Release parameters in various throw-in types remain insufficiently established. This study assessed and compared four types of soccer throw-ins performed in a field environment. Twelve junior soccer players (mean age 13.6±0.6 years, height 1.61±0.21 m, weight 44.42±2.78 kg, and training history 2.14±0.89 years) participated in. The four throw-in skills included two approaches with two feet apart (AFA), feet side by side (AFS), and two standing types (standing with two feet apart -SFA, standing with feet side by side -SFS). Three-dimensional cameras (4K@60 fps) and SkillSpector (version 1.3.2) were used for recording and analysis. Release speed, angle, height, swipe times, and range were evaluated, with correlations assessed from three sets or trials of every player in a total of 144 throw-ins. Results showed higher release speed and average range in approaching and/or stepping types compared to stationary and/or aligned leg types. The average range for (AFA) and (AFS) surpassed (SFS) and (SFA). Release angle (RA) was approximately 33.5° in (AFS), (AFA), and (SFA), while (SFS) exhibited lower values. A predictive equation for ball ranges was developed based on release parameters, including released speed, angle, height, and backwards and forward arm swing times (BAST and FAST).