Kinematic Determinants of Front Kick Dynamics Across Different Loading Conditions

Introduction: The efficiency of front kick is related to the kicking technique. Thus, the aim of this study was to find the kinematic determinants of front kick dynamics across different performance and loading levels (no load to 45-kg load). Materials and Methods: Twenty-four elite and sub-elite professional military personnel (26.8 +/- 10.1 years, 84.2 +/- 5.4 kg, 181.1 +/- 6.4 cm) performed six front kicks into a force plate across five different loading conditions. Three-dimensional kinematics of the kicks was quantified and included velocity of the hip (V-hip), velocity of the knee (V-knee), velocity of the shoulder (V-shoulder), velocity of the foot (V-foot), angular velocity of the knee (AV(knee)), and angular velocity of the hip (AV(hip)). Results: The main kinematic differences between the two groups were that the sub-elite group had an increased kick time for all loading conditions (P<.001) and a lower V-foot (P=.05) and a decreased V-hip and Vshoulder (P<.05) in the highest load condition. V-hip and AV(hip) were the best predictors (up to R-2 = 0.58; P=.020) of peak force and impact force during no-load or loaded kicking at the elite level. Typical predictors of impulse in the elite group were AV(hip), V-hip, and V-shoulder and those in the sub-elite group were AV(knee) and V-foot. Conclusions: The kinematic variables provide good predictions of kicking dynamics; however, the best predictor varies with the loading conditions and performance levels. Hip motion is the main differentiating factor.