The estrogen treatment regimens used in transgender women aim to lower testosterone levels to within the female range (<1 nmol/L) [52]. However, hormone therapy alone has met limited success in suppressing testosterone levels, with many transgender women failing to achieve the desired level. In recent studies of transgender women, one quartile failed to achieve any significant suppression [53] and one-third failed to suppress testosterone levels despite achieving desired estradiol levels [54]. Another study reported that only 49% of transgender women showed suppressed testosterone concentrations after 6 months or more of estrogen with the addition of antiandrogen therapy [55]. Notably, Jarin and colleagues show that testosterone levels in transgender women decreased significantly from former male levels, however nearly all participants maintained their testosterone levels above the female range [56]. Whether elite transwoman athletes experience the same difficulties in suppressing testosterone levels with estrogen therapy has not been reported.