155 Growing up and reaching for the top: A longitudinal study of talented swimmers 7 Yis was the dependent variable (e.g., rMSV) for swimming season s of swimmer i, αi the intercept of swimmer i, Ageis the corresponding age value and High-level performance groupi the dummy variable indicating whether or not swimmer i was in the high-level performance group. The unexplained information was the sum of ui (between-subject variance) and εis (residual variance). The models were validated by using visible patterns in residual plots to check violations of homogeneity, normality and independence. Predictor variables were considered significant if the p value of the estimated mean coefficient was smaller than 0.05. Results Table 1 shows the descriptive statistics, including effect sizes, of male and female swimmers according to their performance level at late junior age (males aged 17; females aged 16) by age group. High-performing late juniors outscored lower-performing late juniors on rST at late junior age (p < 0.001; very large effect sizes), confirming a correct definition of performance level groups in both males and females. Furthermore, high-performing late junior females demonstrated an earlier age of PHV compared to lower-performing females (p <0.05). No significant differences between high- and lower-performing male and female swimmers on age and weekly swim training hours were found (p >0.05). Figure 2 provides a visual representation of the mean scores, interquartile range, as well as the minimum and maximum scores for age of PHV, height, and swim training hours. High-performing late junior males scored significantly higher on rMSV at age 13, 14 and 15 (all p <0.001), rSI at age 13, 14 (p <0.05) and 15 ((p <0.01), and rST at age 13,14 and 15 (all p <0.001), compared to lower-performing peers. The effect sizes for rMSV and rST were found to be very large, while for rSI, they showed an increasing trend from medium to very large. Although not statistically significant, high-performing late junior males had higher scores on CMJ (small-to-medium effect sizes) at age 13, 14 and 15, and height at age 15 (medium effect sizes) compared to lower-performing males. Similar scores were found between groups on height at age 13 and 14 (no effect). High-performing late junior females scored significantly higher on rMSV at age 12, 13 and 14 (p <0.001 at age 12 and 13, p <0.01 at age 14), rSI at age 12 (p < 0.01), CMJ at age 14 (p < 0.05), height at age 13 and 14 (p <0.05) and rSBT at age 12, 13 and 14 (all p <0.001) compared to lower-performing peers. The effect sizes for rMSV and rST were found to be very large while for CMJ and height the effect sizes were considered large. Although not statistically significant, high-performing late junior females had higher scores on CMJ (small-to-medium effect sizes) at age 12 and 13, and height at age 12 (medium-to-large effect sizes) compared to lower-performing females.
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