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SAO PAULO, Brazil — New research conducted by Brazilian scientists reports transgender women's hearts and lungs remain stronger than those of their cisgender peers, even after years of hormone therapy. More specifically, transgender women's heart and lung capacity and strength exceeds that of cisgender women. However, heart and lung capacity and strength levels among transgender women were lower than those of cisgender men.
While this project did not include transgender athletes, study authors still believe that their findings may help inform new policies and decisions moving forward regarding transgender women’s participation in sports.
Exposure to male (testosterone) or female (estrogen) sex hormones during puberty and throughout reproductive life influences physical performance among both men and women. Testosterone usually sparks changes in muscle mass, strength, body fat, and red blood cell capacity. VO2, a measure of how efficiently the body transports and uses oxygen, is typically 50 percent lower among cisgender women in comparison to cisgender men of the same age.
Researchers can't say at this time what impact previous exposure to testosterone may have on the physical efforts and performances of transgender women who aren’t athletes and are undergoing long-term therapy to reduce their natural testosterone levels.
How does hormone therapy affect physical performance?
In an effort to better understand this topic, researchers assessed heart-lung (cardiopulmonary) capacity and strength among 15 transgender women, 13 cisgender men, and 14 cisgender women. Each person was in their mid-thirties and generally engaged in similar physical activity levels.
Participating transgender women had been on hormone therapy for an average of 14 years. On average, these individuals started hormone therapy at the age of 17. The research team measured each person's body fat and muscle mass (bioimpedance). A hand grip test to assess strength was also conducted, in addition to cardiopulmonary exercise testing (VO2) on a treadmill.
Transgender women had lower total body fat levels than cisgender women, but more fat than cisgender men. Similarly, skeletal muscle mass was higher among transgender women in comparison to cisgender women, yet lower than it was among cisgender men.
“Thus, long-term estrogen exposure and testosterone suppression were not enough to completely shift [body composition of transgender women] to the female pattern, despite their direct and indirect effects on fat and lean mass,” researchers say in a media release.
Transgender women had stronger grip strength and average peak VO2 than cisgender women. While these findings are notable, and this is the first project of its kind, researchers caution that at the end of the day this was a small study featuring only non-athletes. Moreover, medications used, doses, and frequencies all relied on personal recall from the participants.
Where do scientists go from here?
Study authors would like future studies to account for, and measure, the start and duration of puberty and muscle cell metabolism. This will help determine the long-term impact of hormone therapy on transgender women’s performance in sport.
“These are the first scientific data on the cardiopulmonary capacity of transgender women,” study authors add. “These findings add new insights to the sparse information available on a highly controversial topic about the participation of transgender women in physical activities.”
The study is published in the British Journal of Sports Medicine.
