Kinematic and kinetic evidence for functional lateralization in a symmetrical motor task: the water polo eggbeater kick.

Bilaterality and motor lateralization have been associated with neural lateralization, suggesting that the dominant and non-dominant systems might have different specializations. The study of symmetrical motor tasks can provide evidence relating to this hypothesis. The water polo eggbeater kick is a skill comprising anti-phase and directionally opposite rotations of the right and left lower limbs to provide upward thrust to elevate the body. Effectiveness of the skill depends on moving the feet in predominantly horizontal directions with an orientation that produces lift throughout as much of the cycle as possible. The purpose of this study was to investigate the motor lateralization of the dominant (D) and non-dominant (ND) lower limbs during the execution of the water polo eggbeater kick technique. Twelve right-handed and right-footed water polo players performed eggbeater kicks in the vertical position to maintain maximum height. Three-dimensional kinematics and the pattern of vertical forces were quantified for nine cycles for each player. The pattern of vertical force produced showed asymmetries between the equivalent phases of the cycles of the dominant and non-dominant limbs (D, 222.8 N; ND, 201.0 N; p < 0.001). Based on the vertical force patterns, the non-dominant ankle had a less efficient motion during the phase of knee flexion (recovery phase). This was a consequence of larger negative pitch angles created by the non-dominant foot for the equivalent phase. Negative pitch angles counteract the lift forces responsible for the upward propulsion of the player. The effectiveness of the dominant side during the recovery phase was a consequence of bilateral differences in rotation and inversion motions by the ankle and hip. Differences in the technique of the dominant and non-dominant side, particularly during the phase of knee flexion, supported the 'dynamic dominance theory' where each hemisphere/limb might be tuned to control different parameters of task performance.