Foot kinematic and kinetic differences associated with eggbeater kick technique: a time-series analysis in water polo...

Eggbeater kicking is essential for maintaining body position and supporting technical actions in water polo, yet the time-specific biomechanical characteristics associated with higher performance remain unclear. This study aimed to identify the characteristics of water polo players with higher eggbeater kicking performance by comparing foot kinematics and kinetics using time-series analysis. Twenty-two male university players performed continuous eggbeater kicking while underwater motion capture and pressure sensors recorded foot movements and pressure distributions. Resultant fluid forces and vertical propulsive forces were estimated using pressure distribution analysis. Participants were allocated into upper and lower groups using a pre-set threshold for normalised propulsive force derived from an independent dataset. Statistical parametric mapping (one-tailed SPM{t}, α = 0.05) was applied to detect time-specific between-group differences. Time-specific differences in dynamic pressure and foot angles were identified mainly during the out-kick phase, whereas no significant differences were observed in foot velocity or acceleration. These findings suggest that the timing of foot orientation adjustments, rather than movement velocity alone, may be an important characteristic associated with propulsion-related performance during eggbeater kicking. The identified critical phases may inform targeted technical training and guide future biomechanical investigations of unsteady propulsion mechanisms.