A study on transgender athletes has found trans females retain up to a 12% advantage in athletic tests even after taking hormones for two years to suppress testosterone levels. The results, researchers suggest, indicate the current International Olympic Committee guidelines may give trans women an “unfair competitive advantage” over biological women.
 
“For the Olympic level, the elite level, I'd say probably two years is more realistic than one year,” said Dr. Timothy Roberts, the director of the adolescent medicine training program at Children's Mercy Hospital in Kansas City, Missouri and the study’s lead author. “At one year, the trans women on average still have an advantage over the cis [biological] women," he stated.  
 
Roberts made these discoveries studying Air Force servicemen and women who were in the process of transitioning. After several months of taking hormones, the men in transition were still able to do more push-ups and run faster than their biologically female counterparts. He explained that while being in the military is a different scenario than being in the Olympics, “it’s a comparable situation, where you have someone doing whatever they can to maintain or improve their abilities.”