Reevaluating the definition of rapid weight loss in sports: a call for change

Pre-competition weight loss (WL) is a widely adopted strategy in weight-sensitive sports, particularly among combat sport. This strategy enables athletes to compete at a weight or weight classes below their habitual body mass (BM). Although research on WL for weight-sensitive sports has steadily grown, it mostly employs the term "RWL". However, there is no compelling or universally accepted definition of RWL. In this current opinion, we discussed the deficiencies and misuse of the current definition of RWL and proposed a new theoretical framework to provide a basis for better defining RWL in the future. A most commonly used definition describes RWL as losing 5% of body mass within 7 days. However, this definition is somewhat arbitrary and lacks empirical justification. This definition is based on two parameters: magnitude (5% BM) and duration (7 days), yet its cut-off remains rigid and lacks empirical support. Several studies on combat athletes have found that a relatively faster rate of WL can lead to significant negative impacts on performance and health variables. We argue that using WL rate as the core criterion is more robust, as the term "rapid" emphasizes the speed of WL. However, at what rate does WL become classified as RWL? The limited research in this area underscores the need for studies to establish a solid foundation for defining RWL. In many studies, authors use the term "RWL," especially in quantitative research. However, using the current definition, some practices reported by participants (e.g., losing 2% BM over 30 days) do not qualify as RWL. Finally, we propose that WL (not RWL) practices be classified along two dimensions: WL rate and WL magnitude. Based on rate, practices can be categorized as slow, moderate, or rapid WL. Based on magnitude, they can be classified as low, moderate, or high WL.