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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.

Due to the difficulty of measuring forces and torques acting on a swimmer during mid-pool swimming, an inverse dynamics approach is required. Personalised body segment parameter (BSP) data enabling calculation of net forces and torques can be obtained using the elliptical zone method. The purpose of this study was to establish the reliability of estimating BSP data of swimmers by the elliptical zone method with segment outlines being traced manually on a personal computer screen. Five assessors digitised the segment landmarks and traced the body segments from front and side view digital photographs of 11 single arm amputee swimmers. Each swimmer was assessed five times by each of the five assessors. The order was fully randomised. Within assessor variability was less than 5% for the segment centre of mass position of all segments, for segment length except the neck (5.2%), and for segment mass except neck (11.9%), hands (Left: 8.1%; Right: 5.8%) and feet (Left: 7.3%; Right: 7.3%). Analysis of mean variability within and between assessors indicated that between assessor variability was generally as large or larger than within assessor variability. Consequently it is recommended that when seeking personalised BSP data to maximise the accuracy of derived kinetics and sensitivity for longitudinal and bilateral within-subject comparisons the individual should be assessed by the same assessor with mean values obtained from five repeat digitisations. This study established that using the elliptical zone method using E-Zone software is a reliable and convenient way of obtaining personalised BSP data for use in analysis of swimming. Key pointsA unique (not been attempted previously) study of reliability of calculating personalised Body Segment Parameter (BSP) data using the elliptical zone methodEstablishes benchmark data regarding the reliability of BSP data for comparison with emerging technologies for obtaining personalised BSP data non-invasively.Provides a description and guidelines for good practice for maximising the accuracy of derived kinematics and kinetics in swimming.The method of body modelling described can also be applied to studies in other sports and in assessing change in health status related to body shape characteristics for sport and non-sport populations.

The glide is a major part of starts, turns and the stroke cycle in breaststroke. Glide performance, indicated by the average velocity, can be improved by increasing the glide efficiency, that is, the ability of the body to minimise deceleration. This paper reviews the factors that affect glide efficiency. In the first part of the review the sources of resistive force are reviewed including surface friction (skin drag), pressure (form) drag and resistance due to making waves (wave drag). The effect of body surface characteristics on the skin drag, the effect of the depth of the swimmer on wave drag, and the effects of posture and alignment, body size and shape on the form drag are reviewed. The effects of these variables on the added mass, that is, the mass of water entrained with the body are explained. The 'glide factor' as a measure of glide efficiency that takes into account the combined effect of the resistive force and the added mass is described. In the second part methods of quantifying the resistive force are reviewed. Finally, the 'hydro-kinematic method' of measuring glide efficiency is evaluated., (Copyright 2009 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.)