Voters in four US states, including Democrat-leaning Colorado and Washington, have backed limits on transgender athletes in girls' sport. Fair rules, or going too far?

What happened

At the US midterm elections, voters in four states approved measures on transgender athletes. Colorado's Proposition 134, passed with about 52%, requires school and college teams to be designated by biological sex or as coeducational. Washington's measure bars transgender girls from girls' K-12 teams and requires eligibility documentation. Arizona's Proposition 318 extends existing limits to private sports groups and adds rules for school bathrooms and locker rooms. Nebraska wrote its existing restrictions into the state constitution. The results came as Democrats won control of Congress.

Why people disagree

Supporters say sex-based categories protect fairness and safety in girls' and women's sport because of physical differences, and argue the results show the issue crosses party lines. Opponents, including LGBTQ groups and Democratic lawmakers, say the measures discriminate against transgender students and stop them playing with their friends, and that eligibility checks could mean invasive scrutiny of young athletes, a concern medical groups have also raised.

What's still unclear

How the eligibility checks will work in practice; Colorado's governor-elect, Phil Weiser, said the measure needs "a long, hard look" before it is put in place. Also unclear: whether court challenges follow, and whether a Democrat-controlled Congress takes up national rules.