“If you look at pure physiology, men definitely have an advantage,” said Polly de Mille, an exercise specialist at the Women’s Sports Medicine Center in New York’s Hospital for Special Surgery. “They have wider lungs, bigger airways, and a bigger heart that will pump more blood with each beat.”

Which brings us back to the pool at Norwood High.

Goodwin has found that several of the boys, who were novice swimmers and struggled to keep up with their more experienced female teammates in the longer events, now appear poised to overtake them. Those veteran girls initially held the edge in longer distances because technique and training can be as crucial as raw power in those events. But with a few years’ training for the male teammates, the traditional gender gap emerged.

Norwood is among a small number of Massachusetts high schools with boys competing on the girl’s swim team. Massachusetts law requires equal access to sports for both genders. Most schools typically offer a fall swimming season for girls, and have both boys’ and girls’ teams in the winter. But some districts, such as Norwood, offer just one team and one season because of budget constraints and having to share a pool with a nearby town, hence the mixed-gender Norwood swim team.

That arrangement created national headlines last fall when a Norwood boy, Will Higgins, smashed a meet record for the girls’ 50-yard freestyle event that was set 26 years earlier, by a female.

Some charged that it was fundamentally unfair for men to compete with women — and strip them of records — given the physiological differences.

Goodwin, Higgins’s coach, is torn.

“As a coach, you are thrilled with the hard work and watching it pay off,” she said. “But it’s going to be harder for the girls on the team.”

That’s because the boys’ increasingly faster times, as they catch up in training, will knock some of their female teammates out of events in local girls’ swim meets.

But the brouhaha from last fall’s upset prompted the Massachusetts Interscholastic Athletic Association to change its rules, and for the first time during the fall season, the small number of boys who compete on girls’ swim teams will only be allowed to compete with other boys in state tournaments. They will have their own mini-tournament, with perhaps a dozen or so competing.

Association spokesman Paul Wetzel said the organization changed the rules for tournaments because it concluded a gender gap continues to exist.