BACKGROUND: Swimming performance depends on the interaction between propulsive and resistive forces, which produces unavoidable velocity fluctuations. Traditional descriptors quantify these variations but do not reflect their mechanical cost. This study analyzed the relative power to velocity variation (rPVV), a novel metric that accounts for hydrodynamic conditions, across the four swimming techniques. METHODS: Fifteen competitive swimmers performed maximal 25 m trials in front crawl, backstroke, breaststroke and butterfly, yielding 34 observations. Velocity was measured with a moving-camera system and active drag was assessed using the velocity perturbation method. Mechanical and kinematic-related variables were computed. Linear mixed-effects models examined the effects of technique and sex, and regression analyses explored relationships between variables. RESULTS: rPVV and PVV presented lower values in the alternated techniques compared to the simultaneous ones (p<0.001), showing a negative non-linear relationship with mean velocity (R²=0.531). PVV increased with intracycle velocity variation (R²=0.950), as well as with mean velocity, and decreased in relative terms (R²=0.531). CONCLUSIONS: Velocity fluctuations impose a substantial and technique-dependent mechanical cost. The rPVV appears to be a meaningful indicator of swimming efficiency, with potential value for technique optimization and performance enhancement.
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