118 Chapter 6 Data processing To enable comparisons among swimmers specialized in different strokes and distances, outcomes were related to meaningful reference values and expressed as a percentage, rather than absolute values (see equation 1). Specifically, swim time was related to the prevailing world record (WR), a method initially introduced by Stoter et al. (2019) in speed skating and subsequently applied in competitive swimming (Post et al., 2020a, 2020b). Lower percentages on relative Swim Time (rST) indicated swim performances closer to the WR. Furthermore, scores on swimming tests were related to the average start time, turn time, clean swimming velocity and SI of male and female finalists at the European Championships in 2021 (Born et al., 2022b). Stroke-specific data of the 100- and 200-m events were used as reference values for sprinters (50-100-m) and middle-distance (200-400-m) swimmers in our sample respectively (see Appendix A). Higher percentages on relative maximal swimming velocity (rSprint) and stroke index (rSI), and lower percentages on relative start- (rStart) and turn time (rTurn), indicate scores more close to the European elite level (set to 100%). For example, the 15-m start time of a junior male freestyle sprinter (6.20s) was related to the average 15-m start time of the 100-m freestyle European male finalists (5.55s), resulting in a relative start time of 111.7% ((6.20/5.55) * 100%). Data selection Rather than considering all observations, we selected the swimmers’ season best rST, rStart, rTurn, rSprint along with the corresponding rSI, and rLBP for further analyses (see Appendix B for number of measurements by performance level group and age category). Any other data were excluded, minimizing the impact of variations in achievements within a season. The median number of between-season observations was n = 3 in males and females. Defining Performance Level Groups A higher- and lower-level performance group were defined according to performance trajectories of international elite swimmers, representing a performance level similar to the top 50 swimmers worldwide of the past 5 years (2017-2022 with the exception of 2020, see Post et al., 2020a). Following the approach adopted in previous studies (Stoter et al., 2019; Post et al., 2020b), the maximum season best rST by age category, sex and swim event of these international elite swimmers was used as performance benchmark (%WR, see Appendix C). Swimmers whose season best rST at early senior age (males aged 18-19; females aged 17-18) fell within the corresponding performance benchmark were categorized
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