I can’t answer this with any medical or professional credibility. I suggest, though, that weights should not be a priority until stroke and technique fundamentals are sound and consistent. I believe the best way to improve speed early in a swimming program is through stroke efficiency. Most of us have seen the scrawny kid with great strokes match or beat the big strong kid with poor technique. Or the small 10 yr. old kid who gets whipped by the 10 yr. old who looks 14 – only to beat him when they are 14 because the small kid had great strokes throughout while the big kid’s power advantage disappeared. A child with great strokes uses less energy to move through the water so they can swim fast for a longer period of time and finish races strongly.

As a parent of high school age swimmers I offer some additional considerations. First the weight training should be coached and guided professionally. Kids do not instinctively know how to lift weights correctly or safely. Many seem to have no idea which muscle is the triceps. So they need guidance. Boys seem to turn weightlifting into a competition. So you have to be careful they don’t get into a bench pressing contest when it has minimal value to swimming.

As for girls vs. boys – we all know girls mature physically sooner than boys. So that suggests that girls could begin weightlifting sooner than boys. But that probably doesn’t happen in swimming where girls and boys of the same age or capability train together.

If a high school age swimmer chooses to lift weights I suggest 2 times a week is the minimum for it to be useful. With no scientific basis to defend this – I suggest no more than 3 times a week. I think it is smart to be conservative with children whose bodies are still changing. If the child wants to spend more time training it might be more productive to spend the time in the water swimming.