, Volume 94, Issue 1-2, pp 134-144
Date: 09 Feb 2005

An energy balance of front crawl

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With the aim of computing a complete energy balance of front crawl, the energy cost per unit distance (C= Ėv −1, where Ė is the metabolic power and v is the speed) and the overall efficiency (ηo =W tot /C, where W tot is the mechanical work per unit distance) were calculated for subjects swimming with and without fins. In aquatic locomotion W tot is given by the sum of: (1) W int, the internal work, which was calculated from video analysis, (2) W d, the work to overcome hydrodynamic resistance, which was calculated from measures of active drag, and (3) W k, calculated from measures of Froude efficiency (ηF). In turn, ηF=W d/(W d+W k) and was calculated by modelling the arm movement as that of a paddle wheel. When swimming at speeds from 1.0 to 1.4 m s−1, ηF is about 0.5, power to overcome water resistance (active body drag × v) and power to give water kinetic energy increase from 50 to 100 W, and internal mechanical power from 10 to 30 W. In the same range of speeds Ė increases from 600 to 1,200 W and C from 600 to 800 J m−1. The use of fins decreases total mechanical power and C by the same amount (10–15%) so that ηo (overall efficiency) is the same when swimming with or without fins [0.20 (0.03)]. The values of ηo are higher than previously reported for the front crawl, essentially because of the larger values of W tot calculated in this study. This is so because the contribution of W int to W tot was taken into account, and because ηF was computed by also taking into account the contribution of the legs to forward propulsion.