Transwomen May Have Lasting Endurance Edge Over Cis-Female Peers

By Anne Harding

December 14, 2020

NEW YORK (Reuters Health) - Transwomen maintain endurance advantages over their cisgender peers even after two years of gender-affirming hormone therapy, according to a new study of Air Force recruits.

On average, transwomen ran 1.5 miles 12% faster than cisgender women (CW) after two years on estrogen, Dr. Timothy A. Roberts of Children's Mercy Division of Adolescent Medicine in Kansas City, Missouri, and colleagues found.

"This study suggests that more than 12 months of testosterone suppression may be needed to ensure that transgender women do not have an unfair competitive advantage when participating in elite level athletic competition," they conclude in the British Journal of Sports Medicine.

World Athletics (IAAF) and the International Olympic Committee (IOC) had established guidelines for transwomen, as well as for women with sexual development disorders causing them to have abnormally high testosterone levels, requiring them to prove their testosterone levels have been adequately suppressed for at least a year before they can compete in events for women, Dr. Roberts and his team note. However, these guidelines as applied to CW with high testosterone were successfully challenged in court due to a lack of evidence.

To better understand how testosterone and estrogen therapy affect athletic performance, the researchers looked at medical records and fitness test results for 29 transmen and 46 transwomen who began hormone treatment while serving in the Air Force, which requires enlistees to undergo physical fitness testing every year.

To date, Dr. Roberts told Reuters Health in a phone interview, more than 400 Air Force members have started gender-affirming therapy since President Obama agreed to cover the treatment for enlisted men and women. This continued under the subsequent administration, although President Trump banned transgender people from joining the military.

Trans study participants completed an average of two fitness assessments before they began treatment with estrogen or testosterone, and were followed for an average of 394 days after they started taking hormones. The authors compared the performance and body composition of these participants with those of all Air Force enlistees under 30 who underwent fitness testing from 2004 to 2014.

Before starting hormone therapy, transwomen could do 31% more pushups and 15% more situps in one minute than CW, and their average 1.5-mile run time was 21% faster. After a year on estrogen, transwomen's pushup and situp performance was similar to CW's, but their 1.5-mile run time was still 9% faster.

At baseline, transmen did 43% fewer pushups than cisgender men (CM) and a similar number of situps, while their run time was 15% slower. With one year of testosterone treatment, these differences disappeared, and transmen were doing more situps per minute than CM.

One year of testosterone therapy is likely enough to even the playing field for trans and cis individuals in recreational and youth athletics, Dr. Roberts said, but it may not be adequate in elite competition.

"For things like archery and equestrian trials it probably doesn't matter that much," he said. "For things like the hundred-meter dash, I think there's probably some retained advantage beyond two years."

He added: "Transmen on testosterone rapidly improved their performance, so they have a distinct advantages."

Dr. Roberts said he and his colleagues would like to follow trans individuals' athletic performance prospectively as they undergo gender-affirming hormone therapy, and are also interested in looking at sports-specific performance measurements.

SOURCE: British Journal of Sports Medicine, online December 7, 2020.