# An energy balance of front crawl

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## Abstract

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* (*η_{o}*=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 (η_{F}). In turn, η_{F}=*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}, η_{F} 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 η_{o} (overall efficiency) is the same when swimming with or without fins [0.20 (0.03)]. The values of η_{o} 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 η_{F} was computed by also taking into account the contribution of the legs to forward propulsion.

## Keywords

Swimming Biomechanics Energetics Propelling efficiency Fins## Notes

### Acknowledgements

The technical assistance of Dean Marky, Frank Modlich and Chris Eisenhardt is gratefully acknowledged, as well as the patience and kind co-operation of the swimmers. This research has been partially supported by the US Navy, NAVSEA, Navy Experimental Unit, contract N61 33199C0028.

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