Joel Stager, a professor in the School of Health, Physical Education and Recreation at Indiana University Bloomington, and colleagues analyzed data provided by USA Swimming that consisted of the best 50-yard freestyle performances for all USA Swimming-registered male and female swimmers ages 6-19, from 2005 to 2010 for a total of 1.9 million swims.
The 50-yard freestyle was chosen because the swimmers' performances were less influenced by training per se and more likely to be influenced by muscle function, Stager explained.
The study found no difference in swim performance in children age 8 and younger and little difference in those ages 11-12.
"It's the whole perception that girls can't compete fairly with boys," Stager said in a statement. "Well, at certain ages, they can."
The effects of puberty began showing in the older swimmers, as the boys began experiencing accelerated growth in height, weight and strength typical of age 13 and older, Stager said.