In summary, key findings and conclusions from the reviews of the social science literature and biological scientific literature include:
1. Sex verification testing of athletes should be considered a human rights violation and eliminated from all levels of sport.
2. Doping control procedures make it virtually impossible for physically born male or female athletes competing at the national level or international level to intentionally cheat by masquerading as the opposite sex.
3. There is no evidence or convincing logic that athletes would transition in order to gain competitive advantages.
4. While generally there are numerous anatomical and physiological differences between men and women, there also is a vast range of anatomical and physiological variation within each sex. The implication is to ask whether transitioned athletes, in fact, fit in the broad variance that already exists within their new sex.
5. Both testosterone and estrogen can influence performance, and therefore transitioning and transitioned athletes participating in competitive sport should try to consistently have sex hormone levels within the normal range for their new sex.
6. Physically born women and transitioned women have similar concentrations of both testosterone and estrogen. Estrogen supplementation to transitioned women resulted in haemoglobin levels similar to those found in physically born women, and similar muscle mass at the upper range of development. Subcutaneous fat content remained lower while total body weight was higher in transitioned women.
7. Transitioned men can have higher estrogen and testosterone concentrations compared with physically born men but the difference in testosterone levels can be eliminated by using a new long-lasting testosterone dosing regime. However, for all approved dosing regimes, testosterone supplementation to transitioned men resulted in haemoglobin levels similar to those in physically born men, and similar muscle mass at the upper range of development even when concentrations were higher. The only difference that continued following one year of supplementation was a higher amount of subcutaneous fat in transitioned men which could diminish performance in competitions with physically born men.
8. To date, there is no available research or other reliable scientific evidence to either support or refute the position that transitioned athletes compete at an advantage or disadvantage compared with physically born men and women athletes. In view of the lack of available research and the methodology requirements for credible new research, the answer to that question may never be known with certainty given the low prevalence of transitioned individuals in the population.
9. The IOC and World Anti-Doping Agency play influential leadership roles in how the sport community views sex and gender issues, and how the sport community sets policies establishing related eligibility and participation criteria.
10. The eligibility requirements in the IOC‘s Stockholm Consensus on sex reassignment in sports should be reviewed considering that few metabolic changes were found beyond one year of cross-sex hormone supplementation. The conditions that are imposed should not be vague or onerous to the point of being barriers. Eligibility requirements also need to address the full range of choices possible for transitioning and transitioned athletes. This includes the choice to have hormone supplementation but not sex reassignment surgery which has additional considerations outside the scope of the literature reviews.
11. The World Anti-Doping Code does not include mandatory standards that address the use of hormone supplementation for transition purposes. This could result in discretionary decisions that might be inconsistent from one case to the next.
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