Net force analysis during streamlined glide, dolphin kick, and front crawl at high velocities in competitive swimming...

This study aimed to identify the optimal transition velocities between streamlined glide (SL), underwater dolphin kick (DK), and front crawl (FC) during high-speed swimming. Ten elite female swimmers performed front crawl and dolphin kick trials in a long-course pool, and repeated the same motions under tethered conditions in a water flume to measure net force. Power-law fitting was applied to model net force as a function of flow velocity across the three movement conditions. The results revealed distinct patterns in the scaling coefficients $\left(A\right)$ and exponents $\left(n\right)$, following the order: $A_{\mathrm{SL}}>A_{\mathrm{DK}}>A_{\mathrm{FC}}$ and $n_{\mathrm{SL}}<n_{\mathrm{DK}}<n_{\mathrm{FC}}$. The fitted net force curves intersected at two velocities, $U_{\mathrm{SL}-\mathrm{DK}}$ and $U_{\mathrm{DK}-\mathrm{FC}}$, and for most swimmers, these intersection velocities exceeded their respective constant velocities, $V_{\mathrm{DK}\_\mathrm{const}}$ and $V_{\mathrm{FC}\_\mathrm{const}}$. These intersection points indicate the optimal timing for initiating propulsive actions to minimise deceleration during the post-start and post-turn phases. A conceptual model was proposed to explain the phase transition strategy based on velocity-dependent net force profiles. Although individual variation was observed, most swimmers exhibited similar trends, supporting the applicability of the model. These findings provide a fluid mechanical perspective for optimising underwater strategies and may contribute to enhanced start and turn performance in competitive swimming.