Sex-based differences in swimming performance in 10-years-old-and-under athletes in short course national competition.

The need for sex-segregated youth swimming is debated. A previous report indicates that male swimmers aged 10-and-under are 1%-2% faster than females in long course freestyle, butterfly, backstroke, and individual medley (IM), but not breaststroke events. Another report indicates that at age 10 males are 1%-2.5% faster than females in long course freestyle events. However, there are no evaluations for short course competitions. Therefore, the top eight performances for both sexes from the National Club Swimming Association Age Group Championships (a short course meet) for the years 2016-2023 in the 10-and-under age group were analyzed. Males were 1.16%-2.63% faster (p < 0.05; effect sizes 0.376-0.596) than females in the 50 yards (yd; 45.7 m), 100 yd (91.4 m), and 200 yd (182.9 m) freestyle, 100 yd backstroke, 50 yd breaststroke, 100 yd butterfly, and 100 and 200 yd IM. There were no significant sex-based differences in the 500 yd (457.2 m) freestyle, 50 yd backstroke, 100 yd breaststroke, or 50 yd butterfly. The individual fastest time for a female was faster than for a male in the 50, 100, and 500 yd freestyle, 50 and 100 yd backstroke, 50 and 100 yd butterfly, and 100 yd IM. Although in eight out of 12 events the individual fastest times were from females, in eight out of 12 events the average male times were significantly faster. The present data suggest that although some exceptional individual 10-and-under female swimmers do exist, their performance is not representative of the typical sex-based differences in swimming performance.