The US swimmer Lia Thomas, who rose to global prominence by becoming the first transgender athlete to win a NCAA college title, is taking legal action in a bid to compete again in elite female sport – including the Olympics. Thomas has not swum since World Aquatics introduced new rules in 2022, which prohibit anyone who has undergone “any part of male puberty” from the female category. Before then, transgender women were able to compete if they lowered their testosterone levels. In a scientific policy document that informed its decision, World Aquatics said that swimmers such as Thomas retained significant physical advantages – in endurance, power, speed, strength and lung size – from undergoing male puberty, even after reducing their testosterone levels through medication.