Fig 1.
Mean swimming velocity from 5 to 18 years of the top 100 fastest US boys (blue circles) and girls (red triangles) for the 50, 100, 200, 400, 800 and 1500m freestyle swimming distances.
Fig 2.
Sex differences in performance of the top 5 places.
The primary plot (heat map) displays the sex differences in swimming velocity (% boy’s swimming velocity) of the top 5 US rankings in each freestyle event distance and age, negative values (red) indicate faster performance of girls. The top displays the mean sex difference across age, and the right plot displays the mean sex difference across swimming event distance.
Fig 3.
Relative performance decline across US ranking.
The decline in swimming performance (% 1st Place) across US ranking for boys (blue) and girls (red; mean ± 95% confidence interval; Panel A). The average annual membership numbers (Panel B) for boys (blue) and girls (red) of USA Swimming. The heat maps (Panels C and D) display the sex differences in swimming velocity of the top 5 US Rankings (Panel C) and the 10th-50th US Rankings (Panel D) using the same color values displayed in Fig 2.
Fig 4.
Correlation of boy’s serum testosterone and sex differences in swimming performance across age.
The mean circulating testosterone concentrations from NHANES database were strongly, linearly correlated with the mean sex difference in swimming performance during the years of rapidly increasing testosterone levels for boys (11 to 17 years; p<0.001, r = 0.990), but not during the years of low testosterone for boys (6 to 10 years; p = 0.500). Each circle represents the mean sex difference in swimming for each age group pooled for all race distances and places (x-axis) and mean circulating testosterone level for boys (y-axis) with the age group denoted using corresponding Arabic numeral within each circle. The colored ellipses represent the standard error of three separate groupings for the correlation analysis, low-testosterone group (6–10 years, red), increasing testosterone group (11–17 years, blue) and plateaued testosterone group (18 years, green).