Effects of gender affirming hormone therapy on exercise performance in transgender athletes

The study of the athletic performance of transgender individuals is a novel endeavour. This thesis begins with a systematic review of the changes induced in non-athletic trans women with gender affirming hormone therapy (GAHT) and how these changes may affect athletic performance. The 3 experimental studies in this thesis use different approaches to quantify the changes in transgender athletic performance with GAHT. A longitudinal case study was undertaken to determine the effect of GAHT on the performance of an international level trans woman cyclist (chapter 3). The cyclist demonstrated an ~15% loss of aerobic capacity with 3 months of GAHT and stable aerobic capacity for the following 9 months of GAHT. This cyclist subsequently demonstrated a 19-33% and 15-30% loss of lower and upper body strength respectively with 18 months of GAHT. A retrospective and prospective survey-based study of the performance of trans athletes pre- and 12-86 months post-GAHT in the sports of athletics, powerlifting and swimming was undertaken (chapter 4). In this study, 9 trans women athletes reported that GAHT was associated with female-typical values of testosterone, oestrogen, haemoglobin, and haematocrit. In the same study, 9 transgender women sprinters, middle- and long-distance runners reported a 15% increase in performance times with 5-86 months of GAHT: the increase was 11, 15 and 18% for the sprinters, middle- and long-distance runners respectively. The collective age-grade scores (AGs; male scores pre-GAHT and female scores post-GAHT) of the 9 runners did not change (p=0.304) with GAHT. There was no significant difference between the pre- and post-GAHT training-adjusted AGs for the sprints [95% CI of (-3.0,4.8)], the middle-distance races [95% CI of (-3.7,0.9)], or the long-distance races [95% CI of (-3.1,1.5)]. A single trans man powerlifter reported a linear (r2>0.81, p<0.036) gain of 32, 33 and 42% squat, deadlift and bench press strength with 39-months of GAHT. Lastly, a cross-sectional study comparing aerobic and strength characteristics of 12 trans and 11 cis women athletes was undertaken (chapter 5). The trans athletes demonstrated 20-36% higher strength and explosiveness across 5 measures (p<0.046). However, when strength and explosiveness were normalized to body mass or fat free mass, there were no intergroup differences (p>0.12). There was also no intergroup difference in countermovement jump height (p=0.649). The 12 trans women athletes did not have higher lactate threshold or relative V̇O2peak than the 11 cisgender women athletes (p>0.18). The absolute V̇O2peak of the trans women (3.19 L·min-1) was not quite significantly higher (p=0.057) than the absolute V̇O2peak of the cis women (2.83 L·min-1), however the effect size was large (d=0.84). The three studies suggest that athletic transgender women may lose more strength with GAHT than non-athletic transgender women but may still maintain a sizable absolute (but not relative) strength advantage over athletic cis women; that athletic transgender women may have little to no remaining post-GAHT advantage over athletic cisgender women in aerobic capacity; and that athletic trans men may have the capability for substantial strength gains with GAHT. These findings have implications for transgender inclusion policies depending upon the demands of the sport.