23 Performance development of top-elite swimmers 2 Defining performance levels and groups Four performance levels were defined; top-elite, elite, sub-elite and high-competitive. Each performance level was characterized by sex-specific limits to account for differences in competition level between males and females (Table 1). The limits were calculated as the mean of 5 rSBTs for the xth swimmer from either the 100m freestyle performance FINA World Ranking Lists of 2014-2018 (FINA, 2018) or the 100m freestyle performance National Ranking Lists of the Netherlands 2014-2018 (Swimrankings, 2018). The limits of the top-elite performance level were based on rSBTs of the 8th male and female swimmer of the FINA World Ranking List 2014-2018 (e.g. rSBT 8th male swimmer 2014 + rSBT 8th male swimmer 2015 + rSBT 8th male swimmer 2016 + rSBT 8th male swimmer 2017 + rSBT 8th male swimmer 2018 / 5) . The other limits were defined so that they represented the 50th male and female swimmer of the FINA World Ranking List 2018 (elite performance level) and the 8th and 50th male and female swimmer of the National Ranking List of the Netherlands of 2018 (sub-elite and high-competitive performance levels respectively). We determined each swimmer’s current performance group by allocating the rSBT of a given season to one of the four performance levels. For example, if a 16 year old boy has a rSBT of 108%, his current performance level corresponds with the limits of the high competitive performance group. Next, we determined each swimmer’s best performance group by allocating the best rSBT ever to one of the four performance levels, meaning that a swimmer either once or multiple times has reached this performance level at any age. For example, if a boy has a best rSBT ever of 105%, his best performance level corresponds with the limits of the sub-elite performance group. A swimmer’s current performance group is a dynamic variable and may change over time, whereas a swimmer’s best performance group remains static. Swimmers with a best rSBT ever outside the limits of the high competitive level (best rSBT>114.1% for males and best rSBT >114.6% for females) were excluded from further analysis (a total of 16,406 observations). Moreover, outliers were excluded (a total of 647 observations) using stem-and-leaf plot, as swimmers might have a poor season due to injury, illness or other reasons, which are not representative for the swim performance of swimmers in the corresponding performance group. Table 2 presents the male/female distribution and the number of observations (i.e., rSBTs per swimming season) for each performance group included for the analysis on swim performance. Table 1. Limits of performance levels for males and females separately. Males Females Top-elite rSBT <102.2% rSBT <102.8% Elite 102.2% <> rSBT < 104.0% 102.8% <> rSBT < 105.5% Sub-elite 104.0% <> rSBT < 107.9% 105.5% <> rSBT < 108.0% High-competitive 107.9% <> rSBT < 114.1% 108.0% <> rSBT < 114.6%
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