In a dramatic turn of events, transgender swimmer Lia Thomas has been banned from competing in the Olympics after losing her high-stakes legal battle to overturn a controversial rule change by World Aquatics.

The 25-year-old American swimmer made history as the first openly transgender athlete to win an NCAA Division I national championship, capturing the women’s 500-yard freestyle event in 2022. However, her triumphant moment sparked a wave of controversy, leading to World Aquatics’ decision to ban anyone who had ‘been through male puberty’ from participating in women’s races—a rule directly impacting Thomas, who began hormone replacement therapy in 2019.

Despite her vigorous contestation of the rule since its introduction in 2022, Thomas faced a crushing blow when the Court of Arbitration for Sport ruled against her on June 12, 2024. The panel of three judges upheld the regulations detailed in World Aquatics’ Competition Regulations, which mandate that transgender women athletes must prove they have not experienced male puberty beyond Tanner Stage 2 or before age 12 to compete in women’s categories.

Specifically, section 5.5.2 of the updated regulations, effective from January 1, 2024, states that athletes must either have complete androgen insensitivity or have suppressed male puberty before age 12 and maintained their testosterone levels below 2.5 nmol/L.