Aannah K.A. McKay, Trent Stellingwerff, Ella S. Smith, David T. Martin, Iñigo Mujika, Vicky L. Goosey-Tolfrey, Jeremy Sheppard, and Louise M. Burke present a 6-tiered Participant Classification Framework to systematically classify individuals based on training volume and performance metrics. The framework categorizes participants into Tier 0 (Sedentary), Tier 1 (Recreationally Active), Tier 2 (Trained/Developmental), Tier 3 (Highly Trained/National Level), Tier 4 (Elite/International Level), and Tier 5 (World Class). This classification system aims to provide a standardized approach for research in exercise, sport, performance, health, and fitness outcomes. The framework can be used both prospectively (during study recruitment) and retrospectively (in systematic reviews and meta-analyses). It considers factors such as sport-specific differences, nationality, gender parity, and age-related considerations, including junior and masters athletes, as well as Paralympic athletes. The framework is designed to be adaptable to various sports and can be implemented with minimal physiological testing. It emphasizes the importance of objective data over subjective terminology and provides a flexible structure that can evolve with the sport and athletic abilities over time. The framework aims to enhance the uniformity and consistency of participant classification in research, ensuring that studies are comparable and that findings are applicable to the intended populations. The authors highlight the need for future adaptations of the framework to better address special populations, including Paralympic athletes and individuals with disabilities. The framework is intended to be widely implemented to improve the classification of participants in research and published articles.Aannah K.A. McKay, Trent Stellingwerff, Ella S. Smith, David T. Martin, Iñigo Mujika, Vicky L. Goosey-Tolfrey, Jeremy Sheppard, and Louise M. Burke present a 6-tiered Participant Classification Framework to systematically classify individuals based on training volume and performance metrics. The framework categorizes participants into Tier 0 (Sedentary), Tier 1 (Recreationally Active), Tier 2 (Trained/Developmental), Tier 3 (Highly Trained/National Level), Tier 4 (Elite/International Level), and Tier 5 (World Class). This classification system aims to provide a standardized approach for research in exercise, sport, performance, health, and fitness outcomes. The framework can be used both prospectively (during study recruitment) and retrospectively (in systematic reviews and meta-analyses). It considers factors such as sport-specific differences, nationality, gender parity, and age-related considerations, including junior and masters athletes, as well as Paralympic athletes. The framework is designed to be adaptable to various sports and can be implemented with minimal physiological testing. It emphasizes the importance of objective data over subjective terminology and provides a flexible structure that can evolve with the sport and athletic abilities over time. The framework aims to enhance the uniformity and consistency of participant classification in research, ensuring that studies are comparable and that findings are applicable to the intended populations. The authors highlight the need for future adaptations of the framework to better address special populations, including Paralympic athletes and individuals with disabilities. The framework is intended to be widely implemented to improve the classification of participants in research and published articles.