INTRODUCTION Underwater undulatory swimming (UUS) has aroused the interest of researchers since some swimmers, starting from the Moscow Olympic Games (1980), achieved very good results by swimming longer and longer distances underwater, until its limitation to 15m after the start and the turn or the recent possibility of using it in the backstroke finish. These limits, however, are sufficient for some swimmers to show great differences over the rest in these underwater phases (Ruiz-Navarro et al., 2022). It is our objective to explore in a "holistic" way, all the biomechanical components that could explain a good performance in UUS. METHODS A sample of male and female swimmers from international and regional level were included in the study and performed at least 2x15 m UUS with adequate rest. Swimmers were marked on the right side of the body and bilateral symmetry was assumed. The UUS was analysed according to Papic et al. (2020) using a pre-trained neural network with a mean test error of 5 mm. A set of custom Python scripts were developed to analyse the kinematic trials. In addition, the Kwon XP software allowed a deeper analysis thanks to its graphical capabilities in the analysis and especially in the vector analysis. Some trials were carried out using a linear encoder to record the instantaneous intra-cycle speed (200Hz), which allowed a more simplified analysis. All coordinates were obtained using 2K video at 100Hz. The kinematic analysis of relevant points such as the tip of the foot, ankle, knee, etc. shows coordination patterns in vertical velocity and acceleration (wave analysis). As a flow visualisation tool, we use injected bubbles and the bubble wall. Wake characteristics such as size, vorticity and inertia are related to kinematics and wave analysis to relate them to the propulsive wake generated. RESULTS Sample of graph results that we are producing to analyse the vertical displacement and velocity vs time, and velocity and acceleration vs time in all the body points.
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