Reliability of the Elliptical Zone Method of Estimating Body Segment Parameters of Swimmers

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.