Evaluating the impact of hormone therapy on the athletic performance of transgender women athletes

A new study from Loughborough University has explored how gender-affirming hormone therapy (GAHT) affects the athletic performance of transgender women athletes.

Most sports are segregated by sex to account for well-established physiological differences between males and females—particularly in endurance, strength, and overall athletic performance. These differences are largely attributed to higher levels of circulating testosterone in males following puberty, which contribute to greater height, lean muscle mass, hemoglobin concentration, and larger heart and lung capacity.

Despite increasing attention on the participation of transgender athletes in sport, little is known about the impact of GAHT on athletic performance in transgender women.

In this Loughborough study—led by the School of Sport, Exercise and Health Sciences—researchers analyzed data from nine transgender women runners and one transgender woman swimmer. All athletes competed in the same sport/events both before and after starting GAHT.

Data were collected at study entry and continued to be collected over 12 months. The dataset included self-report race times, distances, training volume, height, weight, and clinical measures of testosterone, estrogen and hemoglobin concentrations.

The paper, “Longitudinal Performance Changes in Transgender Women Athletes Pre- and Post-Gender Affirming Hormone Therapy,” is published in the European Journal of Sports Science.

Using each athlete’s best performances before and after GAHT initiation, average race times for the runners slowed by approximately 15%, while the swimmer’s performance declined by around 5%, with greater decrements in performance observed in longer versus shorter duration events. In the runners, some of this performance decline was associated with changes in training volume, with higher exercise training volume appearing to slow the GAHT-associated decline in performance.

Hormone levels after GAHT were within typical female ranges for all the athletes.

Dr. Emma O’Donnell said, “Although the exact impact of GAHT on performance remains unclear, our findings suggest that sport type and training load may influence its effects in transgender women. Shorter events like sprints, which rely on strength and power, may be less affected than endurance events such as middle- and long-distance running.

“These results are consistent with prior studies showing modest strength losses after 36 months of GAHT and reduced hemoglobin levels within four months. Hemoglobin is an important factor for endurance performance.

“It is important to acknowledge that the study has limitations, including a small sample size and varied participant age and duration of GAHT exposure. As such, the results should be interpreted accordingly.

“This area of research is still in its early stages, and significantly more work is needed to better understand the effects of GAHT on performance. Without robust evidence, it is difficult for sporting bodies to create informed, evidence-based policies around transgender inclusion in sport.”

A new study from Loughborough University has explored how gender-affirming hormone therapy (GAHT) affects the athletic performance of transgender women athletes.

Most sports are segregated by sex to account for well-established physiological differences between males and females—particularly in endurance, strength, and overall athletic performance. These differences are largely attributed to higher levels of circulating testosterone in males following puberty, which contribute to greater height, lean muscle mass, hemoglobin concentration, and larger heart and lung capacity.

Despite increasing attention on the participation of transgender athletes in sport, little is known about the impact of GAHT on athletic performance in transgender women.

In this Loughborough study—led by the School of Sport, Exercise and Health Sciences—researchers analyzed data from nine transgender women runners and one transgender woman swimmer. All athletes competed in the same sport/events both before and after starting GAHT.

Data were collected at study entry and continued to be collected over 12 months. The dataset included self-report race times, distances, training volume, height, weight, and clinical measures of testosterone, estrogen and hemoglobin concentrations.

The paper, “Longitudinal Performance Changes in Transgender Women Athletes Pre- and Post-Gender Affirming Hormone Therapy,” is published in the European Journal of Sports Science.

Using each athlete’s best performances before and after GAHT initiation, average race times for the runners slowed by approximately 15%, while the swimmer’s performance declined by around 5%, with greater decrements in performance observed in longer versus shorter duration events. In the runners, some of this performance decline was associated with changes in training volume, with higher exercise training volume appearing to slow the GAHT-associated decline in performance.

Hormone levels after GAHT were within typical female ranges for all the athletes.

Dr. Emma O’Donnell said, “Although the exact impact of GAHT on performance remains unclear, our findings suggest that sport type and training load may influence its effects in transgender women. Shorter events like sprints, which rely on strength and power, may be less affected than endurance events such as middle- and long-distance running.

“These results are consistent with prior studies showing modest strength losses after 36 months of GAHT and reduced hemoglobin levels within four months. Hemoglobin is an important factor for endurance performance.

“It is important to acknowledge that the study has limitations, including a small sample size and varied participant age and duration of GAHT exposure. As such, the results should be interpreted accordingly.

“This area of research is still in its early stages, and significantly more work is needed to better understand the effects of GAHT on performance. Without robust evidence, it is difficult for sporting bodies to create informed, evidence-based policies around transgender inclusion in sport.”