Abstract: Overtraining Syndrome (OTS) is a pathological condition characterized by dysfunction across multiple systems, with its hallmark being a paradoxical decline in athletic performance despite increased training load. This paper systematically reviews the evolution of OTS from stress theory to complex systems theory, with a focus on the latest findings from the Endocrine and Metabolic Responses on Overtraining Syndrome research (EROS). The study explores the multiple triggers and pathophysiological mechanisms of OTS, revealing that the factors such as insufficient energy intake, poor sleep quality, excessive cognitive effort, and excessive training load collectively lead to the energy depletion and an imbalance in repair mechanisms, resulting in maladaptive responses in the metabolic, endocrine and immune systems, and ultimately triggering OTS. Additionally, the paper highlights the three-tier diagnostic scoring system developed by the EROS research, and integrates strategies including training load adjustments, dietary optimization, sleep management and psychological interventions. Nine specific preventive recommendations are proposed, aimed at effectively reducing the risk of OTS in athletes.