INTRODUCTION Identifying key predictors of performance obtained from field tests is of particular interest for coaches, performance analysts and athletes. The aim of this study was to verify in-field the association between active drag factor (k), propulsive power (W_prop), propelling efficiency (eta_p), and maximal sprint performance (v_max) in front crawl. METHODS Swimmers of different levels (n=51) performed four all-out semi-tethered front crawl sprints with increasing loads (0.1, 2.0, 4.0, and 6.0 kg) using an electromechanical device (1080 Sprint, Sweden). A linear regression of the semi-tethered force vs swimming speed relationship was used to obtain input parameters for the calculation of Drag, k and W_prop adapting the Velocity Perturbation Method1. The eta_p was obtained from the ratio of the average forward speed and the average tangential hand speed2. A stepwise regression was used to identify the association between the selected parameters and maximal sprint performance in front crawl (alpha =5%). RESULTS Two models predicting v_max were obtained from the stepwise regression: (i) including W_prop (R2=0.797; p<0.001), (ii) including W_prop and k (R2=0.965; p<0.001). The eta_p was excluded by the stepwise regression and, individually, presented a negligible correlation with v_max (r=-0.274; p=0.026). DISCUSSION W_prop and k obtained using a coach-friendly semi-tethered swimming protocol are strongly related to v_max. Despite its importance in converting the total mechanical power into W_prop, and its known correlation with swimming economy (an important determinant of performance in longer distances) the eta_p was not a strong predictor of sprint performance in front crawl.
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