Challenging the principle of "No presumption of advantage" with a focus on testosterone and gender eligibility in sports.

Objectives: To evaluate the scientific validity of the International Olympic Committee's (IOC) 2021 framework principle of "No Presumption of Performance Advantage," which suggests that circulating testosterone levels alone does not confer a competitive advantage. Design: A critical review of existing scientific literature concerning the physiological effects of testosterone and male puberty on athletic performance, complemented by a forward-looking proposal for integrating multi-layered biological and performance data. Method: Relevant peer-reviewed studies were examined, focusing on the role of endogenous testosterone, the long-term effects of male puberty, and performance outcomes among transgender women and athletes with differences in sexual development (DSD). Emphasis was placed on strength, power, and endurance metrics. In addition, we outline the emerging potential of combining wearable sensor monitoring with omics profiling to generate a comprehensive, dynamic evidence base. Results: Evidence consistently shows that male puberty is associated with lasting increases in muscle mass, strength, speed, and endurance due to elevated testosterone. Current evidence also suggests such physiological adaptations may endure even after testosterone suppression, potentially mediated by muscle memory mechanisms such as myonuclei permeance and/or epigenetic changes. If verified, transgender women who experienced male puberty and later reduced testosterone levels retain physical advantages, particularly in strength-based sports. Similarly, athletes with DSD exhibiting male-range testosterone levels also show performance advantages in select events. Conclusions: The IOC's principle of "No Presumption of Performance Advantage" contradicts a substantial body of scientific evidence. While inclusion and fairness are important goals, the framework's rejection of testosterone as a key determinant of athletic performance risks undermining competitive fairness and athlete safety in sex-segregated sports, particularly where strength and power are critical. Acknowledging testosterone as a key determinant of performance, our study proposes a novel multi-layered evaluation framework that integrates real-time sensor data with omics analyses. This innovative approach supports the development of adaptive, context-specific, and ethically grounded policies that promote fair, inclusive, and safe competition while offering a forward-looking roadmap for future policy and research.