This cross-sectional study aimed to compare standard laboratory performance metrics of transgender athletes (transgender men and women) to cisgender athletes (cisgender men and women). The study involved 75 participants, including 19 cisgender men, 12 transgender men, 23 transgender women, and 21 cisgender women. The participants underwent various tests, including body composition, lung function, cardiopulmonary exercise testing, strength, and lower body power assessments. Key findings include: - Transgender women had similar testosterone concentrations to cisgender women but higher oestradiol concentrations. - Transgender women had higher absolute handgrip strength and lower relative jump height compared to cisgender women. - Transgender women had lower forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) ratios, suggesting reduced lung function. - Transgender women had comparable absolute VO2max values to cisgender women but lower relative VO2max when normalized for body weight. - Transgender men had lower absolute handgrip strength and absolute VO2max compared to cisgender men. The study concludes that while longitudinal studies are needed to confirm the effects of gender-affirming hormone therapy on athletic performance, the current findings caution against precautionary bans and sport eligibility exclusions that are not based on sport-specific research. The results highlight the need for a more comprehensive assessment of transgender athletes' physiological profiles and the complexity of their athletic performance.This cross-sectional study aimed to compare standard laboratory performance metrics of transgender athletes (transgender men and women) to cisgender athletes (cisgender men and women). The study involved 75 participants, including 19 cisgender men, 12 transgender men, 23 transgender women, and 21 cisgender women. The participants underwent various tests, including body composition, lung function, cardiopulmonary exercise testing, strength, and lower body power assessments. Key findings include: - Transgender women had similar testosterone concentrations to cisgender women but higher oestradiol concentrations. - Transgender women had higher absolute handgrip strength and lower relative jump height compared to cisgender women. - Transgender women had lower forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) ratios, suggesting reduced lung function. - Transgender women had comparable absolute VO2max values to cisgender women but lower relative VO2max when normalized for body weight. - Transgender men had lower absolute handgrip strength and absolute VO2max compared to cisgender men. The study concludes that while longitudinal studies are needed to confirm the effects of gender-affirming hormone therapy on athletic performance, the current findings caution against precautionary bans and sport eligibility exclusions that are not based on sport-specific research. The results highlight the need for a more comprehensive assessment of transgender athletes' physiological profiles and the complexity of their athletic performance.