The interplay between propelling efficiency, hydrodynamic position and energy cost of front crawl in 8 to 19-year-old swimmers

The aim of this study was to investigate the interplay between the arm stroke efficiency (an index of propelling efficiency, η P ) and the static and dynamic position in water (indexes of hydrodynamic resistance, W d ) in determining the energy cost of front crawl ( C ) during a swimmer’s growth. These three parameters are indeed related by the following equation: where η o is the overall efficiency of swimming. The experiments were carried out on 72 swimmers (38 M and 34 F; 8–19 years) who were asked to swim at 1 m s −1 . The static position in water was assessed by measuring the underwater torque ( T ′); the dynamic position in water by measuring the projected frontal area ( A eff ). The ratio between the average values of the eldest to youngest class of age was 3.84 and 2.27 for T ′, 2.13 and 1.68 for A eff , and 1.13 and 1.24 for η P (in M and F, respectively). The increase in T ′ and in A eff was larger than the increase in efficiency suggesting that, in this age range, C should increase, the more so in M than F. Indeed, C increased by 1.58 in male and 1.17 in female swimmers. Based on the values of C and η P (and assuming a constant value of η o ) it is possible to estimate that, in this age range, W d increases by about 1.97 in male and 1.32 in female swimmers, an increase which is proportional to the observed increase in A eff .