Abstract
The aim of this study was to compute and validate estimation equations for the trunk transverse surface area (TTSA) to be used in assessing the swimmer’s drag force in both genders. One group of 133 swimmers (56 females, 77 males) was used to compute the estimation equations and another group of 131 swimmers (56 females, 75 males) was used for its validations. Swimmers were photographed in the transverse plane from above, on land, in the upright and hydrodynamic position. The TTSA was measured from the swimmer’s photo with specific software. Also measured was the height, body mass, biacromial diameter, chest sagital diameter (CSD) and the chest perimeter (CP). With the first group of swimmers, it was computed the TTSA estimation equations based on stepwise multiple regression models from the selected anthropometrical variables. For males TTSA=6.662*CP+17.019*CSD-210.708 (R2=0.32; Ra2=0.30; P<0.01) and for females TTSA=7.002*CP+15.382*CSD-255.70 (R2=0.34; Ra2=0.31; P<0.01). For both genders there were no significant differences between assessed and estimated mean TTSA. Coefficients of determination for the linear regression models between assessed and estimated TTSA were R2=0.39 for males and R2=0.55 for females. More than 80% of the plots were within the 95% interval confidence for the Bland-Altman analysis in both genders.
Highlights
Swimming is considered as a human locomotion technique in the aquatic environment
Drag force is dependent on several hydrodynamic and anthropometrical variables including velocity, shape, size, surface area and it is similar to the general pressure drag equation (Kjendlie and Stallman, 2008): D
Where D is the drag force [N], ρ is the density of the water [kg.m-3], v is the swimming velocity [m.s-1], S is the projected frontal surface area of the swimmers [cm2] and Cd is the drag coefficient
Summary
Swimming is considered as a human locomotion technique in the aquatic environment.Since water is not a natural environment for human beings, there is a lot of interest regarding its research. Swimming is considered as a human locomotion technique in the aquatic environment. Any body, including humans, travelling in aquatic environment, is submitted to four groups of external forces: (i) weight; (ii) buoyancy; (iii) propulsive forces and; (iv) drag force. Where D is the drag force [N], ρ is the density of the water [kg.m-3], v is the swimming velocity [m.s-1], S is the projected frontal surface area of the swimmers [cm2] and Cd is the drag coefficient (changing according to shape, orientation and Reynolds number). The assessment of the drag force can be done with the swimmers towing in water and without segmental actions (i.e. passive drag) while the subject is making segmental actions to propeller him/herself (i.e. active drag) (Pendergast et al, 2006; Marinho et al, 2009). Numerical solutions use techniques such as computer fluid dynamics (CFD)
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