INTRODUCTION Undulatory underwater swimming (UUS) is of great importance to sport swimming due to its application after the start and turn. Thereby, muscular power generates waves that propagate along the body in a pedal direction. As this 3-dimensional body wave propagates through swimmerfs body (with time), the individul body segments accelerate the surrounding water against the direction of swimming. To substantiate the results and to compare different swimmers, various visualization methods were used, however only using 2-dimensional views (either kick amplitude over time at a fixed location or the kick amplitude over swimming direction at a fixed time). However, no representation exists that simultaneously illustrates information about a variety of significant variables of motion while visualizing the shape of the motion over the time. METHODS To describe the vertical kick amplitude (elongation) the approach of general harmonic onedimensional wve was adapted to: …where x stands for the position/distance along swimmer's body, lambda represents the body wavelength, t the time, T the kick cycle duration and phi the phase. a(x) is the length specific amplitude (depending to the segment location) and B(x) the bias due to the asymmetric amplitude distribution (Hochstein & Blickhan, 2014). RESULTS This quasi-3-dimensional representation of measured data using the surface function z(x,t) vividly visualizes the trajectories of the individual body points, the amplitude trajectories over the distance of the body, the displacement of the amplitudes, the frequency of the motion, the body length, the body shape at a fixed time, and the wavelength of the body wave (Buschhorn, 2022). DISCUSSION The presented method allows to evaluate the human UUS in a graphical way and helps to identify the relationships between the different individual variables or parameters in a compact way. When comparing the representations of different swimmers (or fin swimmers), differences in the execution of the movement and the variables that influence efficiency and speed quickly become apparent. Thus, this method of representation is able to evaluate, visualize, and compare the motion of undulatory swimming.
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