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Research Papers

A “Hydrokinematic” Method of Measuring the Glide Efficiency of a Human Swimmer

[+] Author and Article Information
Roozbeh Naemi

Centre for Aquatics Research and Education, The University of Edinburgh, St Leonard’s Land, Holyrood Road, Edinburgh EH8 8AQ, UKroozbeh.naemi@education.ed.ac.uk

Ross H. Sanders

Centre for Aquatics Research and Education, The University of Edinburgh, St Leonard’s Land, Holyrood Road, Edinburgh EH8 8AQ, UK

J Biomech Eng 130(6), 061016 (Oct 23, 2008) (9 pages) doi:10.1115/1.3002764 History: Received March 22, 2007; Revised May 29, 2008; Published October 23, 2008

The aim of this study was to develop and test a method of quantifying the glide efficiency, defined as the ability of the body to maintain its velocity over time and to minimize deceleration through a rectilinear glide. The glide efficiency should be determined in a way that accounts for both the inertial and resistive characteristics of the gliding body as well as the instantaneous velocity. A displacement function (parametric curve) was obtained from the equation of motion of the body during a horizontal rectilinear glide. The values of the parameters in the displacement curve that provide the best fit to the displacement-time data of a body during a rectilinear horizontal glide represent the glide factor and the initial velocity of the particular glide interval. The glide factor is a measure of glide efficiency and indicates the ability of the body to minimize deceleration at each corresponding velocity. The glide efficiency depends on the hydrodynamic characteristic of the body, which is influenced by the body’s shape as well as by the body’s size. To distinguish the effects of size and shape on the glide efficiency, a size-related glide constant and a shape-related glide coefficient were determined as separate entities. The glide factor is the product of these two parameters. The goodness of fit statistics indicated that the representative displacement function found for each glide interval closely represents the real displacement data of a body in a rectilinear horizontal glide. The accuracy of the method was indicated by a relative standard error of calculation of less than 2.5%. Also the method was able to distinguish between subjects in their glide efficiency. It was found that the glide factor increased with decreasing velocity. The glide coefficient also increased with decreasing Reynolds number. The method is sufficiently accurate to distinguish between individual swimmers in terms of their glide efficiency. The separation of glide factor to a size-related glide constant and a shape-related glide coefficient enabled the effect of size and shape to be quantified.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

The free body diagram of a swimmer in the streamlined position during a horizontal rectilinear passive glide

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Figure 2

The relative standard error of calculation (RSEC), the relative error associated with the consistency assumption (RECA), and the sum of these errors (combined errors) versus numbers of points in each glide interval

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Figure 3

Sample raw displacement data of a horizontal rectilinear glide and the corresponding fit based on Eq. 12 together with the plot of the residuals

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Figure 4

Linear fits representing glide factor versus average velocity for different subjects. The thick lines indicate the corresponding best linear fits for male subjects, and the narrow lines represent the females’ best fits.

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Figure 5

Linear fits representing glide coefficient versus average Reynolds numbers for different subjects. The thick lines indicate the corresponding best linear fits for male subjects, and the narrow lines represent the females’ data.

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Figure 6

The reconstructed velocity versus time for the male subjects

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Figure 7

The reconstructed distance traveled during 0.741s

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